Bioinspired Asymmetric Polypyrrole Membranes with Enhanced Photothermal Conversion for Highly Efficient Solar Evaporation.

Solar-driven interfacial evaporation (SDIE) has attracted great attention by offering a zero-carbon-emission solution for clean water production. The manipulation of the surface structure of the evaporator markedly promotes the enhancement of light capture and the improvement of evaporation performance. Herein, inspired by seedless lotus pod, a flexible pristine polypyrrole (PPy) membrane with macro/micro-bubble and nanotube asymmetric structure is fabricated through template-assisted interfacial polymerization. The macro- and micro-hierarchical structure of the open bubbles enable multiple reflections inner and among the bubble cavities for enhanced light trapping and omnidirectional photothermal conversion. In addition, the multilevel structure (macro/micro/nano) of the asymmetric PPy (PPy-A) membrane induces water evaporation in the form of clusters, leading to a reduction of water evaporation enthalpy. The PPy-A membranes achieve a full-spectrum light absorption of 96.3% and high evaporation rate of 2.03 kg m-2  h-1 under 1 sun. Long-term stable desalination is also verified with PPy-A membranes by applying one-way water channel. This study demonstrates the feasibility of pristine PPy membranes in SDIE applications, providing guidelines for modulation of the evaporator topologies toward high-efficient solar evaporation.

Honeycomb-structured fabric with enhanced photothermal management and site-specific salt crystallization enables sustainable solar steam generation.

The emerging of solar-driven interfacial evaporation provides new opportunities to alleviate the shortage of fresh water resource. Nevertheless, in practical solar desalination, salt precipitation will lead to the decrease of evaporation rate due to reduced light absorption and blocked evaporation channels of evaporator. It still remains a challenge to eliminate salt accumulation and simultaneously maintain high-efficient evaporation. In this work, a solar evaporator was prepared based on reduced graphene oxide and chitosan coated honeycomb-structured fabric (rCHF). The rCHF showed a high light absorbance of 97.2% due to enhanced light trapping of the honeycomb structure and ultra-low thermal conductivity of 0.044 W m-1 K-1. Furthermore, the temperature gradient generated inside the honeycomb unit can induce the Marangoni effect, which led to the site-specific salt crystallization on rCHF in seawater evaporation. As a result, the rCHF realized an excellent solar evaporation rate of 2.02 kg m-2h-1 under one sun irradiation (1 kW m-2). The site-specific salt crystallization on the surface of rCHF ensured stable evaporation even in 20% brine, and the isolated salt can be removed by natural dissolution owing to the excellent hydrophilicity of rCHF. This work provides a new perspective for the design of solar evaporator for practical solar seawater desalination.

HRP-mediated graft polymerization of acrylic acid onto silk fibroins and in situ biomimetic mineralization.

Silk fibroin (SF) can be extensively utilized in biomedical areas owing to its appreciable bioactivity. In this study, biocompatible composites of SF and hydroxyapatite (HAp) were fabricated through in situ biomimetic mineralization process. Graft copolymerization of acrylic acid (AA) onto SF was conducted by using the catalytic system of acetylacetone (ACAC), hydrogen peroxide (H2O2) and horseradish peroxidase (HRP), for enhancing the deposition of apatite onto the fibroin chains. Subsequently, biomimetic mineralization of the prepared fibroin-based membrane was performed in Ca/P solutions to synthesize the organized SF/HAp composites. The efficacies of graft copolymerization and biomimetic mineralization were evaluated by means of ATR-FTIR, GPC, EDS-Mapping, XRD and others. The results denoted that AA was successfully graft-copolymerized with fibroin and formed the copolymer of silk fibroin-graft-polyacrylic acid (SF-g-PAA), and the grafting percentage (GP) and grafting efficiency (GE) under the optimal condition reached to 23.2% and 29.4%, respectively. More mineral phases were detected on the surface of SF-g-PAA membrane after mineralization process when compared to that of the untreated fibroin membrane, companying with an improved mechanical property. According to MG-63 cell viability and fluorescent adhesion assays, the mineralized SF-g-PAA composite showed satisfactory biocompatibility and exceptional adhesive effects as well. The synthetized composite of SF-g-PAA/HAp can be potentially applied in the fields of bone tissue engineering.

Synthesis of silk fibroin-g-PAA composite using H2O2-HRP and characterization of the in situ biomimetic mineralization behavior.

Silk fibroin (SF) as a bioactive protein can offer growth substrates for hydroxyapatite (HAp) deposition. In the current work, graft copolymerization of acrylic acid (AA) onto fibroin chains was carried out using hydrogen peroxide-horseradish peroxidase (H2O2-HRP) catalytic system, SF-g-polyacrylic acid (PAA) membranes was prepared subsequently, followed by in situ biomimetic mineralization in the Ca/P solutions, aiming at promoting the deposition of HAp and endowing the fibroin-based biocomposite with enhanced bioactivity. Meanwhile, p-hydroxyphenylacetamide (PHAD) and methyl acrylate (MA), as the model compounds of tyrosine residues in SF and vinyl monomer were used to disclose the mechanism of graft copolymerization. The data from FTIR and SEC chromatograms indicated that vinyl monomer was successfully graft copolymerized with SF during H2O2-HRP treatment. According to the results of XRD, SEM patterns and EDS-Mapping, mineral phases on the surfaces of SF-g-PAA membranes were detected after different cycles of biomimetic mineralization, and the mechanical property of SF-g-PAA/HAp membrane was noticeably improved. Cell viability and adhesion assays revealed that the composite of SF-g-PAA/HAp exhibited acceptable biocompatibility and outstanding adhesion property. The present work provides a novel method for preparation of the fibroin-based biomaterial for bone tissue engineering.

Self-Crosslinking of Silk Fibroin Using H2O2-Horseradish Peroxidase System and the Characteristics of the Resulting Fibroin Membranes.

Silk fibroin has been widely used in biomedical and clinical fields owing to its good biocompatibility. In the present work, self-crosslinking of fibroin molecules was carried out using the hydrogen peroxide (H2O2)-horseradish peroxidase system, followed by preparation of the fibroin membranes, aiming at improving the mechanical property of fibroin-based material and expanding its applications. P-Hydroxyphenylacetamide (PHAD), as the model compound of tyrosine residues in fibroins, was used to investigate the possibility of horseradish peroxidase (HRP)-catalyzed crosslinking. The results were characterized by means of 1H NMR and UPLC-TQD. The efficacy of enzymatic crosslinking of silk fibroins was examined by determining the changes in the relative viscosity, amino acid compositions, and SEC chromatogram. The obtained data indicated that H2O2-HRP incubation led to PHAD polymerization, and the molecular weight of fibroin proteins was also noticeably increased after the enzymatic treatment. CD and ATR-FTIR spectra revealed that H2O2-HRP treatments had an evident impact on the conformational structure of silk fibroins. The mechanical property and thermal behavior for the modified fibroin membrane were noticeably improved compared to the untreated. Meanwhile, the obtained membrane exhibited good biocompatibility according to the cell growth experiment. The present work provides a novel method for preparation of the fibroin-based materials for biomedical applications.