Biochar based photocatalyst for degradation of organic aqueous waste: A review.

The advancement in the treatment technology for wastewater containing recalcitrant pollutants to lower the overall cost and time of the treatment processes is the prime demand. Biochar (BC) based photocatalyst have proved their potential application in the photo-degradation of a wide range of organic pollutants. The structural and chemical properties of the BC enhance the efficacy of photocatalyst, improving its optical properties with increased stability. This review gives an overview of the progress that occurred during the last five years in BC-based photocatalyst for degradation of recalcitrant organic waste in the aqueous system, emphasizing the role of BC in the photocatalytic performance with a brief discussion regarding the various sources of BC and different strategies used to modify the BC. Further, the critical challenges are discussed, which would be confronted during the scaling up and real-time application in wastewater treatment.

Green Synthesis of Silver-Decorated Magnetic Particles for Efficient and Reusable Antimicrobial Activity.

Metal and metal hybrid nanostructures have shown tremendous application in the biomedical and catalytic fields because of their plasmonic and catalytic properties. Here, a green and clean method was employed for the synthesis of silver nanoparticle (Ag NP)-SiO2-Fe2O3 hybrid microstructures, and biomolecules from green tea extracts were used for constructing the hybrid structures. The SiO2-Fe2O3 structures were synthesized using an ethanolic green tea leaf extract to form Bio-SiO2-Fe2O3 (BSiO2-Fe2O3) structures. Biochemical studies demonstrated the presence of green tea biomolecules in the BSiO2 layer. Reduction of the silver ions was performed by a BSiO2 layer to form Ag NPs of 5-10 nm in diameter in and on the BSiO2-Fe2O3 microstructure. The reduction process was observed within 600 s, which is faster than that reported elsewhere. The antimicrobial activity of the Ag-BSiO2-Fe2O3 hybrid structure was demonstrated against Staphylococcus aureus and Escherichia coli, and the nanostructures were further visualized using confocal laser scanning microscopy (CLSM). The magnetic properties of the Ag-BSiO2-Fe2O3 hybrid structure were used for studying reusable antimicrobial activity. Thus, in this study, we provide a novel green route for the construction of a biomolecule-entrapped SiO2-Fe2O3 structure and their use for the ultra-fast formation of Ag NPs to form antimicrobial active multifunctional hybrid structures.

Biowaste-to-bioplastic (polyhydroxyalkanoates): Conversion technologies, strategies, challenges, and perspective.

Biowaste management is a challenging job as it is high in nutrient content and its disposal in open may cause a serious environmental and health risk. Traditional technologies such as landfill, bio-composting, and incineration are used for biowaste management. To gain revenue from biowaste researchers around the world focusing on the integration of biowaste management with other commercial products such as volatile fatty acids (VFA), biohydrogen, and bioplastic (polyhydroxyalkanoates (PHA)), etc. PHA production from various biowastes such as lignocellulosic biomass, municipal waste, waste cooking oils, biodiesel industry waste, and syngas has been reported successfully. Various nutrient factors i.e., carbon and nitrogen source concentration and availability of dissolved oxygen are crucial factors for PHA production. This review is an attempt to summarize the recent advancements in PHA production from various biowaste, its downstream processing, and other challenges that need to overcome making bioplastic an alternate for synthetic plastic.

Conversion of biogas to methanol by methanotrophs immobilized on chemically modified chitosan.

In this study, chitosan modified with glutaraldehyde (GLA), 3-aminopropyltriethoxysilane (APTES), polyethyleneimine, and APTES followed by GLA (APTES-GLA) as a support material was used to improve methanol production from biogas. Among these support materials, chitosan-APTES-GLA showed the highest increase in immobilization yield and relative efficiency of Methylomicrobium album up to 56.4% and 97.7%, respectively. Maximum cell loading of 236 mg dry cell mass per g-support was observed for M. album., which is 7.7-fold higher than that of chitosan. The immobilized M. album maintained a 23.9-fold higher methanol production compared to free cells after 8 cycles of reuse; it also produced 6.92 mmol·L-1 methanol from biogas that originated from anaerobic digestion of rice straw, thereby validating its industrial application. This is the first report on the immobilization of methanotrophs on chemically modified chitosans to improve cell loading and relative efficiency, and its potential applications in the conversion of greenhouse gases to methanol.

One-step hydrothermal synthesis of magnetic rice straw for effective lipase immobilization and its application in esterification reaction.

Immobilization of industrially important enzymes on supports is important to decrease the cost of the overall enzymatic production procedure. Herein, a novel method for synthesizing a new support, magnetic rice straw (MRS) in one step is reported: rice straw (RS) was soaked with Fe2+ ions and these were further reduced to form embedded Fe2O3 nanoparticles on the RS surface, forming MRS. This material presented a magnetic saturation value of 27.32 emu g-1. Lipase immobilization on MRS resulted in 94.3% immobilization efficiency and 91.3 mg g-1 of enzyme loading, which are higher than immobilization on native RS. The lipase stability was increased approximately 8-fold at 70 °C. The lipase-MRS composite was tested in the esterification reaction of biodiesel production, where it showed prominent reusability. Therefore, this novel and rapid synthesis method can provide ecological and economic support for enzyme immobilization and industrially important product formation.

Antimicrobial Activity of Biosynthesized Silver Nanoparticles Decorated Silica Nanoparticles.

The production of cheap and effective compound for medicinal application is a major challenge for scientific community. So, several biological materials have been explored for the possible application in material synthesis which are useful in biomedical uses. Here, biomolecules from green tea leaves were functionalized on the surface of silicon dioxide nanoparticles (GSiO2 NPs). Next, the decoration silver (Ag) NPs on the surface of the GSiO2 NPs was observed in very short time of incubation in aqueous AgNO3. Ultraviolet-visible spectroscopy confirmed the formation of Ag NPs and the high-resolution transmission and scanning electron microscopies confirmed the decoration of spherical Ag NPs of 10 to 15 nm size on the surface of GSiO2 NPs. The antimicrobial activity of the Ag-GSiO2 NPs was determined against Staphylococcus aureus and Escherichia coli. The Ag-GSiO2 NPs displayed sustainable antimicrobial activity compared to Ag ions. The results indicate the potential value of Ag-GSiO2 NPs in surgical material and food processing.

Enhanced Saccharification and Fermentation of Rice Straw by Reducing the Concentration of Phenolic Compounds Using an Immobilized Enzyme Cocktail.

The production of bioethanol from rice straw can contribute to the rural economy and provide clean fuel in a sustainable manner. However, phenolic compounds, which are mostly produced during acid pretreatment of biomass, act as inhibitors of fermenting microorganisms. Laccase is well known for its ability to oxidize lignin and phenolic compounds derived from lignocellulosic biomass. In the present study, an immobilized enzyme cocktail containing laccase was isevaluated in regard to its ability to enhance the saccharification and fermentation processes by reducing the amount of phenolic compounds produced. Saccharification of rice straw with the laccase-supplemented immobilized enzyme cocktail reduced phenolic compounds by 73.8%, resulting in a saccharification yield of 84.6%. In addition, improved yeast performance was is noted during the fermentation process, resulting in a 78.3% conversion of sugar into ethanol with an ethanol productivity of 0.478 g/L/h. To the best of our knowledge, this is the first description of the use of an immobilized enzyme cocktail comprised of Celluclast 1.5L, ß-glucosidase, and laccase for the production of bioethanol from rice straw. This study details a potential approach to producing biofuels from agricultural biomass, the applicability of which can be improved through up-scaling.

Copper Ferrite Magnetic Nanoparticles for the Immobilization of Enzyme.

In this study, novel, hollow superparamagnetic copper ferrite (CuFe2O4) nanoparticles (NPs) were synthesized by a low-temperature hydrothermal method. The hollow magnetic spheres were characterized by field emission scanning electron microscopy and high resolution transmission electron microscopy to confirm their morphology and size. The hollow NPs were demonstrated as the support for biological materials by the immobilization of Thermomyces lanuginosus lipase on the inner and outer surfaces of the hollow spheres. The immobilization of the enzyme was confirmed by Fourier Transform Infra-red spectroscopy and confocal laser scanning microscopy. The immobilized enzyme was shown to have an immobilization efficiency of 84.5%, with approximately 176 mg g-1 of enzyme loading, for the hollow-NPs support. The immobilized enzyme exhibited high storage and temperature stability. The reusability of the immobilized lipase was more than 80% after 10 cycles of repeated use.

Synthesis of cross-linked protein-metal hybrid nanoflowers and its application in repeated batch decolorization of synthetic dyes.

Herein, we report the preparation of a cross-linked protein-metal hybrid nanoflower (NF) system for laccase immobilization. The immobilized laccase showed effective encapsulation yield and activity recovery of 78.1% and 204%, respectively. The catalytic efficiency (kcatVmax-1) of cross-linked NF (CL-NF) was 2.2-fold more than that of free laccase. The CL-NF also exhibited significantly higher stability towards pH and temperature changes. It exhibited excellent storage stability and tolerance towards solvents and inhibitors as compared with the free enzyme. After 10 cycles of reuses, the NF and CL-NF laccase showed 41.2% and 92.3% residual activity, respectively. The CL-NF showed high oxidation potential, 265% that of the free enzyme, towards phenolic compounds. The CL-NF laccase retained the residual decolorization efficiency of up to 84.6% for synthetic dyes under repeated batch conditions of 10 cycles. These results suggested that the preparation of CL-NF is an effective approach to enhance the enzymatic properties and has great potential in many industrial applications.

SnO2 hollow nanotubes: a novel and efficient support matrix for enzyme immobilization.

A major challenge in the industrial use of enzymes is maintaining their stability at elevated temperatures and in harsh organic solvents. In order to address this issue, we investigated the use of nanotubes as a support material for the immobilization and stabilization of enzymes in this work. SnO2 hollow nanotubes with a high surface area were synthesized by electrospinning the SnCl2 precursor and polyvinylpyrrolidone (dissolved in dimethyl formamide and ethanol). The electrospun product was used for the covalent immobilization of enzymes such as lipase, horseradish peroxidase, and glucose oxidase. The use of SnO2 hollow nanotubes as a support was promising for all immobilized enzymes, with lipase having the highest protein loading value of 217 mg/g, immobilization yield of 93%, and immobilization efficiency of 89%. The immobilized enzymes were fully characterized by various analytical methods. The covalently bonded lipase showed a half-life value of 4.5 h at 70 °C and retained ~91% of its original activity even after 10 repetitive cycles of use. Thus, the SnO2 hollow nanotubes with their high surface area are promising as a support material for the immobilization of enzymes, leading to improved thermal stability and a higher residual activity of the immobilized enzyme under harsh solvent conditions, as compared to the free enzyme.

Rapid synthesis and decoration of reduced graphene oxide with gold nanoparticles by thermostable peptides for memory device and photothermal applications.

This article presents novel, rapid, and environmentally benign synthesis method for one-step reduction and decoration of graphene oxide with gold nanoparticles (NAuNPs) by using thermostable antimicrobial nisin peptides to form a gold-nanoparticles-reduced graphene oxide (NAu-rGO) nanocomposite. The formed composite material was characterized by UV/Vis spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and high-resolution transmission electron microscopy (HR-TEM). HR-TEM analysis revealed the formation of spherical AuNPs of 5-30 nm in size on reduced graphene oxide (rGO) nanosheets. A non-volatile-memory device was prepared based on a solution-processed ZnO thin-film transistor fabricated by inserting the NAu-rGO nanocomposite in the gate dielectric stack as a charge trapping medium. The transfer characteristic of the ZnO thin-film transistor memory device showed large clockwise hysteresis behaviour because of charge carrier trapping in the NAu-rGO nanocomposite. Under positive and negative bias conditions, clear positive and negative threshold voltage shifts occurred, which were attributed to charge carrier trapping and de-trapping in the ZnO/NAu-rGO/SiO2 structure. Also, the photothermal effect of the NAu-rGO nanocomposites on MCF7 breast cancer cells caused inhibition of ~80% cells after irradiation with infrared light (0.5 W cm-2) for 5 min.

Production of Methanol from Methane by Encapsulated Methylosinus sporium.

Massive reserves of methane (CH4) remain unexplored as a feedstock for the production of liquid fuels and chemicals, mainly because of the lack of economically suitable and sustainable strategies for selective oxidation of CH4 to methanol. The present study demonstrates the bioconversion of CH4 to methanol mediated by Type I methanotrophs, such as Methylomicrobium album and Methylomicrobium alcaliphilum. Furthermore, immobilization of a Type II methanotroph, Methylosinus sporium, was carried out using different encapsulation methods, employing sodium-alginate (Na-alginate) and silica gel. The encapsulated cells demonstrated higher stability for methanol production. The optimal pH, temperature, and agitation rate were determined to be pH 7.0, 30°C, and 175 rpm, respectively, using inoculum (1.5 mg of dry cell mass/ml) and 20% of CH4 as a feed. Under these conditions, maximum methanol production (3.43 and 3.73 mM) by the encapsulated cells was recorded. Even after six cycles of reuse, the Na-alginate and silica gel encapsulated cells retained 61.8% and 51.6% of their initial efficiency for methanol production, respectively, in comparison with the efficiency of 11.5% observed in the case of free cells. These results suggest that encapsulation of methanotrophs is a promising approach to improve the stability of methanol production.