Samer Ali Alâshami, Abdullah Al Mamun, Nurulizwa Rashid, Mohammed Al-shami
Microcredit financing is extensively considered as an effective development method for poverty mitigation and women empowerment. Nevertheless, relevant studies reflected opposing outcomes on microfinance effects consisting of positive, zero, and negative impacts. Thus, this research investigated Al-Amal Bankâs microcredit impacts on women empowerment in Yemen, one of the poorest Middle Eastern nations. A panel dataset and primary and secondary data were gathered through household surveys and propensity score matching to restrict intangible variablesâ possible effects. The empirical results revealed that microcredit had a significant positive effect on monthly household incomes and accumulated asset values. Although microcredit facilitated female entrepreneurship and income generation for improved household incomes and expenditure, no influence was found on female household decisions and mobility following the patriarchal system practised in many Arabian nations, including Yemen. Hence, the study finding has theoretically and practically contributed to the body of knowledge in three ways. First, a novel proof of how microcredit interactions affected several Yemeni women empowerment elements was identified. This study also provides new insight into the empowerment theory by explaining how access to microcredit influences numerous features of womenâs economic and social empowerment. Lastly, social and family traditions significantly influenced female attributes and lifestyles by reflecting how communal and family rituals affected microcredit impacts on women empowerment and vice versa. Conversely, this study guides Yemeni policymakers and those from other nations on extending financial services for self-development to reduce poverty and drive women empowerment rather than relying on government and international agencies.
The cutting-edge technology, namely Cloud of Things (CoT) has shaped the existing business process into a new orientation in terms of performance, usability, and reliability. Among different business processes, online education is one of the prime areas where CoT can be used to make it more agile in the context of performance and usability. In this endeavor, a novel methodology has been proposed for an online higher education framework based on CoT. The proposed framework is made agile using Service Oriented Architecture (SOA). Furthermore, in order to make the proposed framework more reliable, a Zero Knowledge Proof (ZKPF) system has been introduced here. The proposed ZKPF algorithm is based on the Hadamard matrix. Experimental results have shown to lay bare the effectiveness of the proposed algorithms.
Ke Huang, Yi Mu, Fatemeh Rezaeibagha, Xiaosong Zhang
Hash function is generally known as symmetric and private for use. However, when applying under public key infrastructure, it immediately yields a notion called chameleon hash function. Based on the chameleon hash, this chapter generalizes and formalizes the notion of public key hash (PKH) scheme by rigorous algorithmic design and security models of indistinguishability and collision-resistance. PKH is another form of the trapdoor commitment, which serves as a basic element for zero knowledge and IND-CCA2 secure public key encryption schemes. Notably, PKH (e.g. chameleon hash) has been recently used to build the redactable blockchain where block hash and transaction are supposed to be redacted without impairing consistency. To begin with, this chapter first review background information of PKH. Then, it instantiates by various PKH schemes: ACH, HCCH, PCH, TUCH and RCH which are mostly from our related works. By rich analysis of algorithmic design and proof techniques of security reduction, this chapter gives more empirical knowledge, insightful instruction and practising sources for the readers to follow. To summarize, PHK is considered as a basic primitive for many other cryptographic schemes. It is an easy starting point for a beginner to follow but can also extend to sophisticated design. The simplicity of the instantiated cases helps the reader quickly grasp and practise proof techniques given in this chapter
Ke Huang, Yi Mu, Fatemeh Rezaeibagha, Xiaosong Zhang
This chapter summarizes all enumerated works to derive some empirical knowledge and generalizes some open problems as future challenges. This chapter concludes as follows: (1). The practical design and analysis of cryptographic schemes for blockchain can address significant problems in blockchain at the algorithmic level. This type of research has received popularity from both global cryptographic community and blockchain developer&s;s community. This research field is the most fast-developing region of all research areas. (2). The intrinsic deficiencies in some traditional cryptographic primitives, like ring signature, IND-CCA2 secure encryption, zero knowledge, etc, prevent the successful application of these primitives in the blockchain. However, tremendous efforts are being made to make these primitives practical and applicable by researchers. Hopefully, we can derive efficient and practically-secure zk-SNARKs or public key schemes as building blocks or overlays for blockchain in the near future.} (3) The formal and rigorous design and analysis of public key cryptographic algorithms matters to the researches and development of blockchain. In cryptographic academia, it is generally recommended to design and analyze cryptographic schemes strictly by practising provable security theory, complexity theory, and proof techniques to validate proposed schemes.
Ke Huang, Yi Mu, Fatemeh Rezaeibagha, Xiaosong Zhang
Privacy preservation is an important topic in the advances of blockchain. Zero-knowledge proof (ZKP) has long been used to achieve zero leakage of private information. Mainly, zk-SNARKs (a variant of ZKP) have been extensively studied and tentatively deployed in building crypto-currencies due to their concise proofs and verification times.} This chapter dives deeply into the study of zero-knowledge proof system. It first reviews the background and knowledge of zero-knowledge. Specifically, it shows sequential instructions to build zk-SNARKs in the generic method. This chapter then reviews three notable works of zero-knowledge proof: GS08, GR16 and CA07 schemes. Concretely, GS08 scheme exploits bilinear maps to build efficient non-interactive zero-knowledge proof. GR16 scheme gives tentative answer to how efficient pairing-based succinct non-interactive arguments of knowledge can be. CA17 scheme investigates two main shortcomings and countermeasure of proposals for ZKCP (a zero-knowledge proof based service). The review of the above schemes helps readers gain empirical knowledge of designing and analyzing ZKP schemes. Finally, this chapter reviews the practical implementation of zk-SNARK in Zcash, its performance and other associated problems. This chapter is summarized as follows: (1) It is not trivial to generate a zk-SNARK. The reader should devote hard works in learning what zk-NARKs is about and how it works. (2) Current ZKP schemes quickly develop and extend to various research fields}. The analysis of ZKP scheme generally does not involve complex or skilled proof techniques. However, to fully figure out the meanings of many notations and terms, the reader} ought to follow specific research line and keep track of relevant works. (3) Due to complex and sophisticated design, it is generally infeasible to derive practical zk-SNARK. Meanwhile, the assumption of an honest setup or entity to initiate system parameter contradicts blockchain&s;s decentralization. Therefore, a true ZKP scheme or variant (like zk-SNARK) designed for blockchain should overcome the above problems.
Verifiable delay functions have found a lot of applications in blockchain technology in recent times. Continuous verifiable delay functions are an improvement over the basic notion of VDFs with recursive capabilities. We are proposing the application of VDF for constructing more space time-efficient provers and simulators required for the iterative non-interactive zero-knowledge systems.
Gongxian Zeng, Meiqi He, Siu Ming Yiu, Zhengan Huang
Abstract Electronic voting (e-voting) has been studied for many years. Recently, researchers find that blockchain can provide an alternative secure platform for e-voting systems, because of its properties of tamper resistance and transparency. However, existing blockchain-based schemes either require central authorities to tally ballots or can only handle a limited number of voters. This paper tries to propose a self-tallying e-voting system, i.e. the public can verify the validity of all ballots and tally the ballots without a centralized authority. To achieve this goal, we solve two challenges, namely how to cancel out all random numbers used for ballots and to prove the validity of ballots using a non-interactive zero knowledge proof. Our scheme is proved to be secure and shown to be practical by experiments.
Diego F. Aranha, Sebastian Berndt, Thomas Eisenbarth, Okan Seker ¡ 7 authors
We study masking countermeasures for side-channel attacks against signature schemes constructed from the MPC-in-the-head paradigm, specifically when the MPC protocol uses preprocessing. This class of signature schemes includes Picnic, an alternate candidate in the third round of the NIST post-quantum standardization project. The only previously known approach to masking MPC-in-the-head signatures suffers from interoperability issues and increased signature sizes. Further, we present a new attack to demonstrate that known countermeasures are not sufficient when the MPC protocol uses a preprocessing phase, as in Picnic3.We overcome these challenges by showing how to mask the underlying zero-knowledge proof system due to KatzâKolesnikovâWang (CCS 2018) for any masking order, and by formally proving that our approach meets the standard security notions of non-interference for masking countermeasures. As a case study, we apply our masking technique to Picnic. We then implement different masked versions of Picnic signing providing first order protection for the ARM Cortex M4 platform, and quantify the overhead of these different masking approaches. We carefully analyze the side-channel risk of hashing operations, and give optimizations that reduce the CPU cost of protecting hashing in Picnic by a factor of five. The performance penalties of the masking countermeasures ranged from 1.8 to 5.5, depending on the degree of masking applied to hash function invocations.
Open access
Cryptographic Implementations and Security
Chaos-based Image/Signal Encryption
Physical Unclonable Functions (PUFs) and Hardware Security
E-commerce platforms incorporate reputation systems that allow customers to rate suppliers following financial transactions. Existing reputation systems cannot defend the centralized server against arbitrarily tampering with the supplierâs reputation. Furthermore, they do not offer reputation access across platforms. Rates are faced with privacy leakages because rating activities are correlated with privacy (e.g., identity and rating). Meanwhile, raters could be malicious and initiate multiple rating attacks and abnormal rating attacks. Determining how to address these issues have both research and practical value. In this paper, we propose a blockchain-based privacy-preserving reputation system for e-commerce platforms named RepChain; our system allows cross-platform reputation access and anonymous and private ratings. Using RepChain, all e-commerce platforms collaborate and share usersâ reputations by co-constructing a consortium blockchain and modeling the rating process as a finite state machine. In particular, we facilitate one-show anonymous credentials constructed from two-move blind signatures to protect customersâ identities and resist multiple rating attacks, leverage zero-knowledge range proof to verify the correctness of ratings and defend against abnormal rating attacks, design a secure sum computation protocol among nodes to update reputations, and verify ratings via batch processing and consensus hashes. Finally, we demonstrate the security and privacy of RepChain via a formal analysis and evaluate its performance based on Ethereum test network.
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IoT group communication allows users to control multiple IoT devices simultaneously. A convenient method for implementing this communication paradigm is by leveraging software-defined networking (SDN) and allowing IoT endpoints to âadvertiseâ the resources that can be accessed through group communication. In this paper, we propose a solution for securing this process by preventing IoT endpoints from advertising âfakeâ resources. We consider group communication using the constrained application protocol (CoAP), and we leverage Web of Things (WoT) Thing Description (TD) to enable resourcesâ advertisement. In order to achieve our goal, we are using linked-data proofs. Additionally, we evaluate the application of zero-knowledge proofs (ZKPs) for hiding certain properties of a WoT-TD file.
The amount of information generated grows as more and more sensor and IoT devices are deployed in smart cities. It is of utmost importance for us to consider the privacy data leakage and compromised identity from both outside adversaries and inside abuse of data access privilege. The security assumption of the system should not solely rely on the fact that permission and access control were being implemented correctly. Quite the contrary, a system can be designed in a way that user's identity data and usage traces are not leaked even if the system had been compromised. Based upon our previous on-street parking system utilizing Bluetooth Low Energy (BLE) beacons, we applied a cryptographic primitive called zero-knowledge proof to our authentication system. A commitment scheme and Merkle tree is combined in the setup to achieve zero-knowledge set membership proof. Doing so, the user is anonymous to the server between authentication sessions, while the server's still able to verify the legitimacy of such user. The on-street parking system is therefore immune to privacy data leakage, as for now one cannot mass-query and profile certain user's traces within the system.
Early power stations in China have been in operation for a long time. Due to the limitations of design, construction materials and technological level at that time, many hydroelectric generators have some defects. The computer monitoring and control system of a hydropower station refers to the measurement, control, protection and monitoring of the entire equipment of a hydropower station completed and realized by the computer system. The computer monitoring and control system of hydropower station replaces the traditional control equipment, fault recording equipment, monitoring and measuring equipment and relay protection equipment. This paper studies the full homomorphic encryption algorithm, introduces the zero-knowledge proof technology into the block chain trading protocol based on the full homomorphic encryption, and constructs the block chain that protects data privacy.
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
Cybertwin-driven-based network architecture for sixth generation (6G) is a new cloud-centric network architecture, which was put forward to address challenges of 6G, such as scalability, security, mobility, and availability. As more and more users’ data are obtained and converted into other digital asset by the cybertwin, relevant techniques of data management to enhance privacy and security becomes a key challenge for Cybertwin-driven 6G. The double authentication preventing ring signature (DAPRS) is a cryptographic primitive that meets requirements of authenticity, anonymity of users’ private data, and linkability of users’ misbehavior, so it is suitable for monitoring behaviors of risky users. In this article, we propose a post-quantum secure ring signature to enhance security and privacy in Cybertwin-driven 6G (PRSG). In the PRSG, we first put forward an accumulator based on a chameleon hash function that allows to efficiently prove knowledge of an accumulated value. Then, we construct a DAPRS based on the accumulator and the zero-knowledge argument of knowledge. Finally, we present how to use the DAPRS to build a secure and efficient privacy-preserving scheme in the Cybertwin-driven 6G. Security proof shows that this scheme achieves anonymity, unforgeability, as well as double signature extractability. Also, we make some security analysis and performance evaluation to demonstrate that the PRSG has low communication complexity, high performance, and privacy preservation in the cybertwin-driven 6G.
Random algorithms have a unique place in complexity theory as a model of computation that ispotentially more powerful than ânormalâ algorithms, and is also practical. However, it is still notclear how much more power randomness adds. The primary goal in studying random algorithmsis derandomization â some method to simulate random algorithms without actually using random-ness. While full derandomization is quite difficult, we show some weak derandomization results âone using advice, and one using multi-pseudodeterminism. We show that improving these resultswould have major implications. Finally, we show new containments and oracle separations betweentraditional random classes and zero-knowledge proofs.
In recent years, the Internet of Things (IoT) has been contemplated as the next technological advancement in the era of data communication and networking. However, although hundreds of new IoT platforms are introduced to the market every few months, the security of IoT ecosystems is still not fully understood. This paper discloses the architecture of a multilayer, multimode security system for the IoT. The proposed system is capable of providing multiple security solutions that support anonymous authentication, device privacy, data integrity, device sybil attack detection and IoT server spoofing attack detection. For IoT access control and authentication, our system can support two modes of operations, with one mode endorsing device privacy protection over the network and the second mode relinquishing device identity to establish data tracing during safety-critical IoT events. The new security system includes two innovative crypto approaches, zero knowledge proof (ZKP) and blockchains. IoT device anonymity was achieved via the multimode ZKP protocol, while data integrity and protection against sybil and IoT spoofing attacks were maintained via blockchains. Our threat analysis models showed that data modification and data injection attacks are not feasible. Probabilistic modeling of an IoT spoofing attack was performed in this paper, and the results show that our security system provides high resiliency against such attacks, with a probability approaching 1.
Nowadays, Smooth Projective Hash Functions (SPHFs) play an important role in constructing cryptographic tools such as secure Password-based Authenticated Key Exchange (PAKE) protocol in the standard model, oblivious transfer, and zero-knowledge proofs. Specifically, in this article, we focus on constructing PAKE protocol; that is, a kind of key exchange protocol which needs only a low entropy password to produce a cryptographically strong shared session key. In spite of relatively good progress of SPHFs in applications, it seems there has been little effort to build them upon quantum-resistant assumptions such as lattice-based cryptography and code-based cryptography to make them secure against quantum computer attacks. More precisely, there are two proposals based on lattice assumptions that utilize the SPHFs to construct PAKE secured in standard model. Considering quantum-resistant assumptions is less than straightforward and needs some relaxations. In this article, we introduce two new Approximate SPHF (ASPHFs) from error-correcting codes. Upon designing ASPHF, we can construct two efficient PAKE protocols. The security of our protocols could be proved based on the hardness of bounded decoding (BD) problem and learning with parity (LPN) problem in the standard model.
We propose a technique to construct physical Zero-Knowledge Proof (ZKP) protocols for puzzles that require a single loop draw feature. Our approach is based on the observation that a loop has only one hole and this property remains stable by some simple transformations. Using this trick, we can transform a simple big loop, which is visible to anyone, into the solution loop by using transformations that do not disclose any information about the solution. We illustrate our technique by applying it to construct physical ZKP protocols for two Nikoli puzzles: Slitherlink and Masyu.
We consider the problem of efficiently inferring interventional distributions in a causal Bayesian network from a finite number of observations. Let $\mathcal{P}$ be a causal model on a set $\mathbf{V}$ of observable variables on a given causal graph $G$. For sets $\mathbf{X},\mathbf{Y}\subseteq \mathbf{V}$, and setting ${\bf x}$ to $\mathbf{X}$, let $P_{\bf x}(\mathbf{Y})$ denote the interventional distribution on $\mathbf{Y}$ with respect to an intervention ${\bf x}$ to variables ${\bf x}$. Shpitser and Pearl (AAAI 2006), building on the work of Tian and Pearl (AAAI 2001), gave an exact characterization of the class of causal graphs for which the interventional distribution $P_{\bf x}({\mathbf{Y}})$ can be uniquely determined. We give the first efficient version of the Shpitser-Pearl algorithm. In particular, under natural assumptions, we give a polynomial-time algorithm that on input a causal graph $G$ on observable variables $\mathbf{V}$, a setting ${\bf x}$ of a set $\mathbf{X} \subseteq \mathbf{V}$ of bounded size, outputs succinct descriptions of both an evaluator and a generator for a distribution $\hat{P}$ that is $\varepsilon$-close (in total variation distance) to $P_{\bf x}({\mathbf{Y}})$ where $Y=\mathbf{V}\setminus \mathbf{X}$, if $P_{\bf x}(\mathbf{Y})$ is identifiable. We also show that when $\mathbf{Y}$ is an arbitrary set, there is no efficient algorithm that outputs an evaluator of a distribution that is $\varepsilon$-close to $P_{\bf x}({\mathbf{Y}})$ unless all problems that have statistical zero-knowledge proofs, including the Graph Isomorphism problem, have efficient randomized algorithms.
Abstract This paper presents HashWires, a hash-based range proof protocol that is applicable in settings for which there is a trusted third party (typically a credential issuer) that can generate commitments. We refer to these as âcredential-basedâ range proofs (CBRPs). HashWires improves upon hashchain solutions that are typically restricted to micro-payments for small interval ranges, achieving an exponential speedup in proof generation and verification time. Under reasonable assumptions and performance considerations, a Hash-Wires proof can be as small as 305 bytes for 64-bit integers. Although CBRPs are not zero-knowledge and are inherently less flexible than general zero-knowledge range proofs, we provide a number of applications in which a credential issuer can leverage HashWires to provide range proofs for private values, without having to rely on heavyweight cryptographic tools and assumptions.
Fuchang Xu, Dehui Weng, Xiang Li, Yang Li ¡ 5 authors
Open AccessCCS ChemistryRESEARCH ARTICLE14 Jul 2022Self-Healing Hydrophilic Porous Photothermal Membranes for Durable and Highly Efficient Solar-Driven Interfacial Water Evaporation Fuchang Xu, Dehui Weng, Xiang Li, Yang Li and Junqi Sun Fuchang Xu State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012 , Dehui Weng State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012 , Xiang Li State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012 , Yang Li *Corresponding author: E-mail Address: [email protected] State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012 and Junqi Sun State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012 https://doi.org/10.31635/ccschem.021.202101111 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail It is highly desirable to develop a solar-driven interfacial water evaporator with a self-healing ability and high-efficiency water evaporation performance for water distillation and desalination; however, this process is considerably challenging. Herein, by exploiting the advantages of a self-healing hydrophilic polymer, a self-healing hydrophilic porous photothermal (SHPP) membrane was fabricated by curing a mixture of the polymer, carbon black, and NaCl, followed by removal of the NaCl from water. Since the SHPP membrane could serve as a photothermal layer and water transportation channel simultaneously, a solar-driven interfacial evaporator could be fabricated readily by assembling the SHPP membrane with polyethylene foam. We have shown that the SHPP membrane-based evaporator exhibited a water evaporation rate of 1.68 kg mâ2 hâ1 and an energy efficiency of 97.3%. These values are superior to those obtained using solar-driven interfacial evaporators with self-healing capability. Notably, by hydrogen bonds reformation between the fracture surfaces, the SHPP membrane could regain its structural integrity after breaking, making the SHPP membrane-based evaporator the first to heal entirely and repeatedly from physical damage to sustain its water evaporation capacity. Therefore, the potential of using SHPP membranes to develop stable, long-lasting, and high-efficiency solar-driven interfacial water evaporators is highlighted. Download figure Download PowerPoint Introduction Fresh water, accounting for only 3% of the total water resources on earth, is vital to human survival and social development. However, with increased population, as well as persistent environmental pollution, the shortage of fresh water has become a key global issue. Therefore, it is imperative to develop effective technologies to generate fresh water from seawater or sewage.1â3 Among all the water treatment technologies, solar-driven evaporation has attracted extensive research attention due to the environment-friendly and renewable characteristics of solar energy.4 Recently, solar-driven interfacial water evaporation, which minimizes thermal dissipation and applies most of the heat to the liquidâvapor phase transition by concentrating heat at the waterâair interface, has been developed to improve the water evaporation efficiency.5â17 Generally, most of the reported solar-driven interfacial evaporators comprise three parts18,19 (Scheme 1a1: (1) a photothermal layer with broadband light absorption and high photothermal conversion, (2) a floatable supporting layer with low thermal conductivity, and (3) a hydrophilic water channel either on the outside or in the middle of the supporting layer that ensures a continuous water supply to the photothermal layer. Although many high-efficiency solar-driven interfacial evaporators have been developed, in practical applications, the photothermal layer or water channel can be damaged by scratching or corrosion, thereby deteriorating the water evaporation efficiency (Scheme 1a2). Hence, to satisfy the requirements for practical applications, it is critical to develop solar-driven interfacial evaporators with a stable water evaporation efficiency. In particular, it is crucial to develop solar-driven interfacial evaporators that can maintain their water evaporation performance after damage. Scheme 1 | (a) Schemes of (1) the composition of a typical solar-driven interfacial evaporator and (2) the loss of its water evaporation capacity due to damage to the water transportation channel. (b) Schematics of (1) the composition of the SHPP membrane-based solar-driven interfacial evaporator and (2) its ability to restore the water evaporation ability via self-healing after physical damage. Download figure Download PowerPoint With the progress in supramolecular chemistry and synthetic chemistry, various self-healing polymers capable of healing damage by themselves to restore the mechanical and/or chemical properties have been synthesized successfully.20â23 In addition, by combining self-healing polymers with functional materials, plenty of self-healing functional materials with superhydrophobicity,24â27 antifouling,28â30 electrical conductivity,31â34 sensing,35â41 and other functions42â50 have been fabricated, decreasing maintenance costs and promoting safety, reliability, and service life significantly. The design and fabrication of self-healing materials with photothermal and water transportation capabilities, able to repair their functions upon damage, would be a judicious solution to increase the stability and service life of solar-driven interfacial evaporators. Although our group and a few other researchers have reported the fabrication of self-healing photothermal membranes for solar-driven water evaporation, these membranes can only heal chemical damage.51,52 Furthermore, the water evaporation rates of these self-healing photothermal membranes were not ideal (<1.31 kg mâ2 hâ1), related to their hydrophobic/superhydrophobic nature that hindered water transportation and evaporation. Previously, our group reported that self-healing superhydrophobic porous materials with a photothermal conversion ability capable of healing physical damage could be obtained using a self-healing hydrophobic polymer and carbon nanotubes as the main materials using NaCl as the template.53 Based on the experience in self-healing porous materials fabrication, along with the widely available knowledge in hydrophilic self-healing polymer synthesis, a rational selection of the material composition was made that led to self-healing hydrophilic photothermal membranes with long-term advantages of high-efficiency evaporation capability for solar-driven interfacial evaporators. As a proof of concept, for the first time, we are reporting a self-healing hydrophilic porous photothermal (SHPP) membrane for highly efficient solar-driven interfacial water evaporation based on a carefully designed and synthesis of a self-healing hydrophilic polymer. The SHPP membrane was fabricated by curing a mixture of self-healing hydrophilic polymer with carbon black (CB) and NaCl, followed by removing the NaCl from water. By tuning the hydrophilicity of the self-healing polymer and the mass ratios of the feed materials, the water content of the SHPP membrane that considerably affects the water evaporation performance could be controlled. From the self-healing perspective, the self-healing polymer permitted the coalescence of the cut SHPP membrane via the reformation of hydrogen bonds between the fracture surfaces, leading to the healing of structural integrity. As the SHPP membrane could simultaneously serve as the photothermal layer and water transportation channel, a highly efficient solar-driven interfacial evaporator can be readily fabricated by assembling the SHPP membrane with a polyethylene (PE) foam (Scheme 1b1). By floating such a designed evaporator on the water surface, the evaporation rates of lake water and seawater reached 1.67 and 1.61 kg mâ2 hâ1, respectively. When the water evaporation capacity of the evaporator was lost by cutting the SHPP membrane, it was able to self-heal at room temperature, and the water evaporation performance of the evaporator was fully restored (Scheme 1b2). Moreover, the SHPP membrane was capable of healing damage caused at the exact location repeatedly without losing the water evaporation performance. The simple structure of the SHPP membrane-based evaporator benefits its integration into conventional solar distillation devices. In this study, we fabricated a prototype distillation device comprising an SHPP membrane-based evaporator to demonstrate the applicability of the SHPP membrane for sewage purification and seawater desalination. Experimental Methods Materials PE glycol (PEG; Mw = 1000) and polyvinyl alcohol (PVA; Mw = 85,000â124,000, 87â89% hydrolyzed) were purchased from Sigma-Aldrich (Shanghai, China). Polytetramethylene ether glycol (PTMG; Mw = 1000) was purchased from Aladdin (Shanghai, China). Dicyclohexylmethane 4,4-diisocyanate (DMDI; purity < 90%) was purchased from TCI Development Co., Ltd. (Shanghai, China). Dibutyltin dilaurate (DBTDL; purity < 97.5%) was purchased from J&K Scientific Ltd. (Beijing, China). Tetrahydrofuran (THF) was purchased from Innochem Science & Technology Co., Ltd. (Beijing, China). CB was purchased from Alfa Aesar Chemical Co., Ltd. (Shanghai, China). Anhydrous ethanol and NaCl were purchased from Beijing Chemical Reagents Company (Beijing, China). All of the chemicals were used without further purification. Synthesis of PUx A series of PUx with different molar ratios of PEG and PTMG were synthesized by the step-growth polymerization of PEG, PTMG, and DMDI. Taking PU50 as an example, PEG (5.00 g, 5 mmol) and PTMG (5.00 g, 5 mmol) were added into a 250 mL three-neck round-bottom flask equipped with mechanical agitation, nitrogen inlet, and condensation reflux. The reaction was allowed to proceed under vacuum for 2 h at 100 °C; then the system was cooled to 60 °C and filled with nitrogen gas. Subsequently, THF (100 mL), DMDI (3.15 g, 12 mmol), and DBTDL (0.05 g, 0.08 mmol) were added into the three-neck round-bottom flask. After 48 h of stirring at 60 °C under nitrogen, the reaction solution was purified by dialysis using a dialysis membrane [molecular weight cutoff (MWCO), 8000â14,000 Da] with anhydrous ethanol. Finally, PU50 was obtained after ethanol evaporation. PU0, PU10, PU20, PU30, and PU40 were synthesized separately in accordance with the method described above. Fabrication of PUx/CBm/NaCln membranes CB and NaCl with different mass ratios were mixed for 30 min using a ball mill machine. Next, CB and NaCl blends were added to 15 mL THF solutions of PUx (the concentration of PUx depended on the composition of PUx/CBm/NaCln), followed by mechanical stirring at 500 rpm for 1 h to ensure that CB and NaCl were well dispersed in the PUx solutions. The resulting solution mixtures were poured into Teflon molds and cured at room temperature. After complete removal of THF, the exteriors of the solidified composite blocks were rubbed with sandpaper and immersed in water baths renewed every 6 h over 2 days to remove the NaCl completely with the resultant PUx/CBm/NaCln porous membranes. The water-soaked PUx/CBm/NaCln porous membranes were wiped with filter papers and then dried at room temperature. Characterization The Mw and PDI of PUx were characterized on a Shimadzu gel-permeation chromatography (GPC; Shimadzu, Japan) system. THF was used as the moving phase, and the flow rate was 1.0 mL minâ1. Fourier transform infrared (FT-IR) spectra were taken on a Bruker VERTEX 80 V FT-IR spectrometer (Bruker, Germany). The differential scanning calorimetry (DSC) curves of PUx were obtained on a TA instrument Q200 (TA, USA) at the heating/cooling rate of 10 °C minâ1 in a N2 atmosphere. Simulated solar light was provided by a PL-XQ500W xenon lamp (Beijing Springs Technology Co., Ltd., Beijing, China), and the light intensity was kept at 1000 W mâ2. Temperature values and IR images of the samples were captured using a HIKVISION H10 thermal imager (HIKVISION, Hangzhou, China). The distance between the sample and the thermal imager was fixed at 20 cm. The accuracy in temperature of the thermal imager is Âą2 °C. The reflection and transmission spectra of the samples were characterized by a UV-3600 spectrophotometer (Shimadzu, Kyoto, Japan). The optical images and videos were captured using a Canon PowerShot SX40 HS camera (Canon, China). The scanning electron microscopy (SEM) images were obtained using a JEOL JSM 6700F field emission scanning electron microscope (JEOL, Japan). The optical microscopy images were obtained using an Olympus DP72 optical microscope (Olympus, China). The porosity (Ď) of the PUx/CBm/NaCln porous membrane was calculated by the following equation: Ď = ( M wet â M dry ) / ( M wet â M sub ) (1)where Mdry is the dry mass of the membrane, Mwet is the mass of the prewetted membrane measured in air, and Msub is the mass of the membranes soaked in water. The solar thermal conversion efficiency (Ρ) of the PUx/CBm/NaCln porous membrane was calculated by the following equation: Ρ = H e Ă ( ν Total â ν Dark ) / Q s , (2)where He is the heat of water evaporation (2260 kJ kgâ1), Qs is the incidence light power, νTotal is the evaporation rate of the PUx/CBm/NaCln porous membrane at stable state under one sun irradiation, and νDark is the evaporation rate of the PUx/CBm/NaCln porous membrane in dark environment. To test its water transport capacity, a piece of PUx/CBm/NaCln porous membrane (0.1 cm Ă 1 cm Ă 5 cm) was partially immersed in a beaker containing 50 mL of deionized (DI) water, and a piece of filter paper was used to absorb water from the upper end of the membrane continuously. The filter paper was replaced after it was saturated with water. The water flux (F) of the PUx/CBm/NaCln membrane was calculated by the following equation: F = M water / ( S * t ) , (3)where Mwater is the mass change of the DI water in the beaker, S is the cross-sectional area of the membrane, and t is the test time. Results and Discussion The self-healing hydrophilic polymer that was key for fabricating the SHPP membrane with a stable, highly efficient solar-driven interface water evaporation capability was synthesized by the step-growth polymerization of PEG, PTMG, and DMDI, as shown in Figure 1a. The resulting polymers were denoted as PUx, where x referred to the molar percentage of PEG in the total monomers. A peak characteristic of âN=C=O at 2268 cmâ1 was not observable in the FT-IR spectra of PUx ( Supporting Information Figure S1). Meanwhile, peaks corresponding to the C=O stretching vibration, as well as NâH stretching and bending vibrations, were observed around 1720 and 1533 cmâ1, respectively, confirming the successful synthesis of PUx. GPC was employed to estimate the weight-average molecular weight (Mw) and polydispersity index (PDI) of PUx. Supporting Information Table S1 lists the results. Although the molar ratios of PEG and PTMG were different, all of the PUx exhibited similar Mw and PDI. In this study, hydrophobic PTMG and hydrophilic PEG were used rationally by adjusting the molar ratio of the two monomers due to the regulation of hydrophilicity of PUx. With an increase in the PEG content, the water uptake of PUx increased, indicating that the hydrophilicity of PUx increases with an increase in the molar ratio of PEG ( Supporting Information Figure S2). Figure 1 | (a) Synthetic route of PUx. (b) Photographs of the PU20 film after being cut and being healed at room temperature for 6 h. (c) Microscopy images of the cut PU20 membrane before and after healing for 6 h at room temperature. (d) Stressâstrain curves of the pristine PU20 film and the cut PU20 film after healing for different times at room temperatures. The stretching speed was 50 mm minâ1. Download figure Download PowerPoint Taking PU20 as a representative, the self-healing ability of PUx was examined. A piece of the PU20 film (0.6 cm Ă 3.5 cm) was cut in half with a knife, and the two parts were subsequently reattached closely (Figure 1b). After placing the PU20 film under ambient conditions for 6 h, the separated PU20 film was conglutinated together, restoring its structural integrity. In addition, an optical microscopy image confirmed that the cut was healed completely (Figure 1c). The self-healing ability of PU20 was attributed to its abundant reversible hydrogen bonds and low glass transition temperature (â51.3 °C, Supporting Information Figure S3). When the fracture surfaces were brought into close contact, the polymer chains migrated gradually into the voids, and the hydrogen bonds reformed with one another, leading to healing of the cut.54 Tensile tests were employed to characterize the healing ability of PU20 further. As the healing time increased, the fracture stress of the healed PU20 film increased gradually and recovered to 4.26 MPa after 6 h of healing at room temperature (Figure 1d). Accordingly, the healing efficiency of PU20, defined as the proportion of the restored fracture stress to the original stress, was calculated to be 98.4%, indicating a satisfactory self-healing ability. In addition, the self-healing abilities of PUx with different PEG contents were examined. Supporting Information Table S2 lists the results. With an increase in the PEG content, the healing efficiency of PUx increased due to the reduction in Young's modulus of the resulting polymer via an increase in the PEG segments ( Supporting Information Table S2). With the successful synthesis of PUx, SHPP membranes were fabricated using PUx, CB, and NaCl. CB was used due to its good photothermal conversion ability and low costs,55,56 while NaCl was used as a sacrificial template. The self-healing hydrophilic porous PUx/CBm/NaCln membranes, where m and n represent the mass ratios of CB and NaCl to PUx, respectively, were fabricated by casting a dispersion of PUx, CB, and NaCl in THF into a Teflon (R) mold, followed by solvent evaporation and NaCl removal in water (Figure 2a). Owing to the simple fabrication, a piece of PU20/CB0.5/NaCl5 membrane with dimensions of 11 cm Ă 11 cm was obtained readily (Figure 2b). The SEM image in Figure 2c reveals that the PU20/CB0.5/NaCl5 membrane exhibits a three-dimensional interconnected hierarchical porous structure, comprising a CB-reinforced PU20 skeleton and macropores with diameters ranging from 9.7 to 109.8 Îźm. Based on Archimedes' method (eq 1), the porosity of the PU20/CB0.5/NaCl5 membrane was 59.8%. Figure 2 | (a) Schematic of the fabrication processes of the PUx/CBm/NaCln membranes. (b) Photographs of the PU20/CB0.5/NaCl5 membrane. (c) Cross-section SEM image of the PU20/CB0.5/NaCl5 membrane. (d) Photograph showing that the PU20/CB0.5/NaCl5 membrane transported water to a height of 5 cm in 3 min. (e) Photograph of the PU20/CB0.5/NaCl5 membrane-based solar-driven interfacial evaporator. (f) Temperature changes of DI water and the PU20/CB0.5/NaCl5 membrane-based evaporator floating on the DI water under simulated solar light irradiation. (g) Time-sequence IR images of the DI water-filled glass containers without (left) and with (right) the PU20/CB0.5/NaCl5 membrane-based evaporator under simulated solar light irradiation for (1) 1 min and (2) 60 min. (h) The mass changes of the DI water with and without the PU20/CB0.5/NaCl5 membrane-based evaporator under simulated solar light irradiation. Download figure Download PowerPoint The combination of the hydrophilicity of PU20 and the porous structure permitted a 5 cm vertical transport of water by the PU20/CB0.5/NaCl5 membrane due to capillary force (Figure 2d), qualifying it to be a water transportation channel. In addition, the average transmittances and reflections of the PU20/CB0.5/NaCl5 membrane were close to zero in the wavelength range from 200 to 2500 nm ( Supporting Information Figure S4). The intense light absorption of the PU20/CB0.5/NaCl5 membrane was related to the excellent light absorption performance of the CB in a broad wavelength range and the porous structure. This further improved the solar-energy harvesting efficiency via a reduction in light reflection.57 Next, the photothermal ability of the PU20/CB0.5/NaCl5 membrane was investigated by irradiating the membrane with a simulated solar light (1000 W mâ2), then an IR camera was used to monitor the temperature of the membrane in air. Under light irradiation, the temperature of the PU20/CB0.5/NaCl5 membrane increased rapidly to 57 °C in 1 min and then reached a steady-state temperature of 70 °C by 5 min ( Supporting Information Figure S5), demonstrating an excellent photothermal ability. As the PU20/CB0.5/NaCl5 membrane simultaneously exhibited excellent water transport and photothermal abilities, we envisioned that a simple efficient solar-driven interfacial water evaporator could be readily by the PU20/CB0.5/NaCl5 membrane a PE foam to serve as a and an layer simultaneously (Figure The water evaporation performance of the PU20/CB0.5/NaCl5 membrane-based evaporator floating on the water was measured by placing the evaporator in a DI water-filled glass on an Simulated light with an intensity of 1000 W mâ2 was on the PU20/CB0.5/NaCl5 membrane surface, and the water mass change was Under light irradiation, the PU20/CB0.5/NaCl5 membrane light and the water The temperature of the PU20/CB0.5/NaCl5 membrane rapidly increased to °C in 1 min and reached a steady-state temperature of °C by 5 min (Figure and Since the PU20/CB0.5/NaCl5 membrane transported water from the glass to the of the evaporator (Scheme this membrane-based evaporator exhibited a water evaporation rate of 1.68 kg mâ2 hâ1 (Figure to 2 provided in the Experimental the solar thermal conversion efficiency of the PU20/CB0.5/NaCl5 membrane-based evaporator was 97.3%. we that such a high solar thermal conversion efficiency for the evaporator was related to the that most of the heat was used to the water at the of the evaporator and that only a of the heat was to the water the glass As after 1 h of simulated light irradiation, the temperature of the water under the evaporator only increased by 5 °C (Figure In the temperature of water in the glass without the PU20/CB0.5/NaCl5 membrane-based evaporator increased by °C after 1 h of simulated light irradiation (Figure Owing to the low light absorption capacity of water and water the evaporation rate of water in the glass without the evaporator was only kg mâ2 hâ1 (Figure with the of the PU20/CB0.5/NaCl5 membrane-based the evaporation rate of water increased Subsequently, the of the composition of the PUx/CBm/NaCln membranes on the performance of the PUx/CBm/NaCln membrane-based evaporators was examined. the membranes with x being were As with an increase in PEG content, the hydrophilicity of PUx the membrane-based evaporators were floating on the water, the membrane water content increased with PEG content of PUx (Figure By an increase in PUx hydrophilicity hindered water flow the membrane, the water flux of the membrane as the PEG content Notably, with an increase in the PEG content, the water evaporation rate of the membrane-based evaporators increased and then water content and water flux of and kg mâ2 hâ1, the water evaporation rate reached a of 1.68 kg mâ2 hâ1 (Figure Next, the water evaporation rates of the membrane-based evaporators were (Figure As the NaCl content was increased, the water content and water flux of the membrane This was as increased NaCl content increased the membrane porosity ( Supporting Information Figure with an increase in water content and water a NaCl to PU20 mass ratio of the PU20/CB0.5/NaCl5 membrane-based evaporator exhibited the water evaporation Finally, the of the CB content on the performance of the membrane-based evaporators was (Figure We observed that the PU20/CB0.5/NaCl5 membrane exhibited the water content and water confirming that the PU20/CB0.5/NaCl5 membrane-based evaporator the water evaporation This is at an low CB content, the in the resulting membrane ( Supporting Information Figure thereby leading to a in porosity ( Supporting Information Figure water content, and water flux (Figure the other to its CB led to a in the water content and water flux of the membrane (Figure our that PU20 was the mass ratios of CB to PU20 and NaCl to PU20 were at and respectively, and the PU20/CB0.5/NaCl5 membrane-based evaporator exhibited the water evaporation rate of 1.68 kg mâ2 Therefore, in the following study, the PU20/CB0.5/NaCl5 membranes were used to the self-healing solar-driven water evaporator. Figure 3 | Evaporation water and water content of the PUx/CBm/NaCln membrane as a of (a) the molar ratio of PEG, (b) the mass ratio of NaCl, and (c) the mass ratio of (d) changes of the simulated seawater and lake water with PU20/CB0.5/NaCl5 membrane-based evaporators under simulated solar light irradiation. Download figure Download PowerPoint The water evaporation rates of the PU20/CB0.5/NaCl5 membrane-based evaporator floating on lake water and simulated seawater from DI water, were examined. With the of the the evaporation rates of the lake water and simulated seawater were 1.67 and 1.61 kg mâ2 hâ1, (Figure The corresponding solar thermal conversion were and is a that all solar-driven evaporators seawater desalination. from the good of the PU20/CB0.5/NaCl5 membrane, the seawater evaporation rate of the PU20/CB0.5/NaCl5 membrane-based evaporator was at kg mâ2 hâ1 after h of seawater evaporation, which was times that of simulated seawater ( Supporting Information Figure Moreover, the seawater evaporation of the evaporator was recovered by 10 mL of seawater the PU20/CB0.5/NaCl5 membrane ( Supporting Information Figure These that the PU20/CB0.5/NaCl5 membranes potential in sewage purification and seawater desalination. the stability of the PU20/CB0.5/NaCl5 membranes was examined. We that the porosity of the PU20/CB0.5/NaCl5 membranes was after in and NaCl solutions for 10 indicating that the membranes exhibited satisfactory Moreover, the porosity of the PU20/CB0.5/NaCl5 membranes was well after placing in the or in water at 50 °C for 10 days ( Supporting Information Figure and Figure indicating that the porous structure in the membranes was highly These that the PU20/CB0.5/NaCl5 membranes good stability and could with the of solar-driven interfacial evaporators. Figure | changes of the PU20/CB0.5/NaCl5 membranes after being