Bioreduction Method Research Articles

Hyaluronate macromolecules reduced-stabilized colloidal palladium nanocatalyst for azo contaminated wastewater treatment

Palladium nanoparticles (PdNPs) are of great important catalysts for a wide variety of applications. With the increasing demands of these materials, green and novel synthesis methods have become one of the leading research focuses. In obedience to the principle of an eco-friendly approach, PdNPs were developed following a one-pot green synthesis technique using sodium hyaluronate (SH) as reductant and stabilizer, which is a non-toxic, renewable, and glycosaminoglycan polymer. The synthesis protocol was spectroscopically monitored to achieve an optimum reaction condition using a one-variable-at-a-time technique where all parameters (concentration of SH, media pH, reaction time, and temperature) were tested in a set of experiments. The growth of PdNPs was evinced from intense brown color in the reaction solution and broad continuous absorption spectra in the UV–vis region. The synthesized PdNPs coated with SH-macromolecules were face-centered cubic crystal structure (d-spacing = 0.233 nm) with spherical/oval shape, uniformly polydispersed (ranged from 2.1 to 8.6 nm), smaller in size (5.3 ± 2.1 nm), and highly stabilized (zeta potential = −25.0 mV). The homogeneous catalytic performance of PdNPs exhibited almost 100% dye degradation for reactive red 195 and reactive yellow 145 by 12 and 16 min with a kinetic-constant value of 0.2128 and 0.1505 min –1 , respectively. The practical application of as-synthesized biogenic PdNPs as a nanocatalyst could be explored for the eco-friendly environmental treatment of wastewaters polluted with toxic, mutagenic, and hazardous azo dyes/pigments. • This bioreduction method is capable of synthesizing PdNPs by green and fast approach. • Hyaluronate is used as a soft matrix and reducing-stabilizing agent for PdNPs synthesis. • The high yield of the PdNPs is achieved using a one-variable-at-a-time optimization strategy. • Synthesized PdNPs are nano-sized, spherical shape, uniformly polydisperse, highly stable, and FFC crystal structure. • The synthesized PdNPs possessed excellent catalytic reduction potential against toxic azo dyes.

Antioxidant and Antimicrobial Activity of Protein-AgNPs from the Stem of Nicotiana Tabacum

Background: Stems of Nicotiana tabacum have secondary metabolites with antimicrobial and antioxidant properties. The purpose of the present study was to investigate the therapeutic properties of synthesized silver nanoparticles (Protein-AgNPs) in an isolated protein mixture from stems. Methodology: A N. tabacum protein mixture was used for the formation of silver nanoparticles by the bioreduction method. Characterization of Protein – AgNPs was completed using UV-Vis spectroscopy, Dynamic Light Scattering (DLS), Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM). Therapeutic properties of Protein-AgNPs were evident with antimicrobial and antioxidant activities. The antimicrobial activity of Protein-AgNPs was determined by the agar well diffusion and broth diffusion methods. The mode of action of Protein-AgNPs was determined by the cellular membrane leakage assay. Antioxidant activities of Protein-AgNPs were quantified by Superoxide Dismutase activity (SOD), Catalase activity (Cat), Glutathione S Transferase activity (GST), Glutathione Content (GSH) and lipid peroxidation. Results: The synthesized Protein-AgNPs were less than 100nm as characterized by UV-Vis spectroscopy, DLS, AFM and SEM. Antimicrobial activity was observed against both Gram positive and Gram negative bacteria, revealing maximum antimicrobial activity against Staphylococcus aureus and Acinetobacter baumannii (p value ≤ 0.05) as determined by the agar well diffusion method and the broth dilution method. The mode of action is likely to be cellular membrane damage, because protein and nucleic acid leakage was significant in treated cells. The antioxidant activities of Protein-AgNPs were higher than purified proteins as determined by Superoxide Dismutase activity (SOD), Catalase activity (Cat), Glutathione Stransferase activity (GST), Glutathione content (GSH) and lipid peroxidation. Conclusion: Synthesized silver nanoparticles from a tobacco stem protein mixture can be utilized as a herbal remedy or as a nano-drug delivery system against diseases such microbial pathogens.

Phytochemical mediated synthesis of silver nanoparticles and their antibacterial activity

In this present work, we described a bio-reduction method for the generation of silver nanoparticles (AgNPs) using aqueous leaf extract of Micrargeria wightii (M. wightii), which is a gifted alternative to other physicochemical routes. The prepared AgNPs were characterized by UV–visible spectroscopy (UV–vis), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (X-RD), Transmission Electron Microscopy (TEM) with EDX and Dynamic light scattering (DLS). UV–visible spectrum showed a characteristic absorption peak at 440 nm of synthesized AgNPs. FT-IR analysis confirmed the existence of plant metabolites, which are responsible for the reduction of Ag (I) ions into Ag (0) NPs. X-RD pattern studies confirm the presence of the pure face-centered cubiccrystalline nature of Ag. Energy-dispersive X-ray (E-DX) spectrum showed the elemental composition of synthesized nanoparticles. Furthermore, TEM images confirm the formation of spherical shaped nano-silver particles with sizes ranging from 30 to 70 nm and supported by particle size analyzer, Dynamic Light Scattering (DLS). Thus, the present investigation provides an easy, eco-friendly and straightforward route for the synthesis of the antibacterial agent against Bacillus subtilis subtilis and Pseudomonas aeruginosa, with 15 and 13 mm zone of inhibition (ZOI) respectively.

Green synthesis of Cuminum cyminum silver nanoparticles: Characterizations and cytocompatibility with lapine primary tenocytes

Current treatment systems for tendon injuries are very few and do not ensure complete cure. This is a serious health concern for sports persons and the aged population. It is known that the nano- or microsized particles of natural products such as jeera/cumin seed (Cuminum cyminum) has been used traditionally as a home remedy for the treatment of tendon injuries. Nevertheless, these particles are likely to perform better due to their smaller size, increased absorption and local delivery in conjunction with nanotechnology. In this context, the major objective of this study was to synthesize silver-capped nanoparticles using aqueous extract of Cuminum cyminum (CCE) and to assess their in vitro non-cytotoxic effect with the perspective of clinical application to enhance tendon tissue regeneration. The presence of phytochemicals in CCE was studied by qualitative and quantitative methods. Cuminum cyminum nanoparticles (CCNP) were synthesized by the bioreduction method using silver nitrate and the particles were characterized by X-ray diffraction analysis (XRD), Fourier Transform Infra Red Spectroscopy (FTIR), Zeta potential measurement and scanning electron microscopy (SEM). The antioxidant effect of the particles was studied using total antioxidant activity and reducing power assay. Simultaneously, primary Tenocytes were isolated from rabbit Achilles tendon by collagenase and dispase digestion/treatment and characterized for Type 1 collagen. Further, in vitro non-cytotoxicity of the CCNP in direct contact with L929 mouse fibroblast cells and primary Tenocytes, respectively, was evaluated by MTT assay. Physico-chemical characterizations confirmed the formation and stability of the nanosize of CCNP with antioxidant property. Again, MTT assay confirmed the non-cytotoxicity of CCNP with L929 fibroblasts and primary Tenocytes. CCNP may be attributed as an ideal candidate for therapeutic application towards a faster restoration of worn-out/injured tendon tissue confronted by the geriatric and athlete communities.

Preparation and properties of cellulose nanocomposite fabrics with in situ generated silver nanoparticles by bioreduction method

The aim of the present study was to develop antibacterial cellulose (cotton) nanocomposite fabrics (CNCFs) with in situ generated silver nanoparticles using medicinal plant Vitex leaf extract. The developed CNCFs were characterized by scanning electron microscope (SEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and antibacterial tests. Further, these CNCFs possessed good antibacterial activities. These CNCFs prepared using simple and environmentally friendly method can be considered for medical applications in, such as, surgical aprons, wound cleaning, wound dressing, and hospital bed materials.

Properties of Biocomposite Films From PLA and Thermally Treated Wood Modified with Silver Nanoparticles Using Leaf Extracts of Oriental Sweetgum

The technological, thermal, and antimicrobial properties of biocomposite films produced from polylactic acid (PLA) and thermally treated wood flour with in situ generated nanosilver particles (AgNPs) using a bio-reduction method. The extracts of fresh leaves of the phenolic-rich Oriental sweetgum (Liquidambar orientalis) tree were used as the reducing agent for silver ions. Six different formulations of the mixed raw materials were extruded in the co-rotating twin screw extruder. The PLA bicomposite films at the 5 and 10 wt% loading levels of wood flour were produced by a hot press method from the following six formulations: (a) thermally treated wood + leaf extract + AgNO3, (b) untreated wood + leaf extract + AgNO3, (c) thermally treated wood + AgNO3, (d) untreated wood + AgNO3, (e) thermally treated wood, (f) untreated wood, and (g) neat PLA. All biocomposite films produced with the untreated/treated wood flour at 5 and 10 wt% loading levels of wood flour showed better tensile modulus than the neat PLA specimens. In general, the tensile strength of the biocomposites was negatively affected by the increased content of the wood flour. The spectra obtained from scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX) showed the silver nanoparticles in the wood particles. The results showed that the biocomposite films produced with PLA and wood flour modified using silver nitrate and leaf extract had the highest tensile modulus. It was observed that the leaf extract treatment had a positive effect on the tensile properties of the biocomposite films at 10 wt% content of wood flour. The remarkable antimicrobial results was obtained by the prepared biocomposites treated with gram positive and gram negative clinical pathogens at maximum zone of clearance 2.6 mm treated with E. coli bacteria.

Ultrasound aided heterogeneous Fenton degradation of Acid Blue 15 over green synthesized magnetite nanoparticles

Magnetite nanoparticles were synthesized by bio-reduction method using neem leaf extract and its structural, morphological, chemical and magnetic characteristics were examined. The characteristic peaks obtained at 30.17°, 35.62°, 43.22°, 53.73°, 57.16° and 62.87° in the X-ray diffraction pattern (XRD) confirmed the formation of magnetite nanoparticles. Batch experiments were conducted to examine the efficiency of magnetite nanoparticles for degradation of the dye, Acid Blue 15 (AB15) by Fenton and ultrasound aided Fenton process. The results revealed enhanced dye removal in ultrasound aided Fenton mode when compared to Fenton process as degradation was attained within 20 min of contact time in the former process. Further, operational parameters on ultrasound aided Fenton degradation of AB 15 were optimized. Total organic carbon (TOC) removal efficiency and dye removal efficiency obtained was 40.4% and 99.3%, respectively at an optimum condition of pH 3, catalyst dosage 1 g L-1, H2O2 dosage 10 mM, and initial AB15 dye concentration of 100 mg L-1. Leached iron concentration at the end of the reaction was determined to be 0.60 mg L-1. The catalyst possesses good stability as it exhibited good performance over 3 cycles. The involvement of hydroxyl radicals in the degradation was confirmed by conducting experiments using radical scavengers. Gas chromatography mass spectrum (GC–MS) analysis revealed the formation of 4-((4-ammoniocyclohexa-2,5-dien-1-ylidene)(phenyl)methyl)aniline, N-ethyl-N-methylethanamine and 3- methylbenzenesulfonate as by-products of ultrasound aided Fenton process. Hence, ultrasound aided Fenton process is a promising method to degrade organic pollutants in wastewater.

BIOREDUCTION AND CHARACTERIZATION OF SILVER NANOPARTICLES FROM OIL PALM EMPTY FRUIT BUNCH

BIOREDUCTION AND CHARACTERIZATION OF SILVER NANOPARTICLES FROM OIL PALM EMPTY FRUIT BUNCH (OPEFB). The synthesis of silver nanoparticles was successfully carried out by extracting oil palm empty fruit bunch. The precursor used was silver nitrate (AgNO3) with a concentration of 9x10-4 M and 5 wt% of the oil palm empty fruit bunch extract. OPEFB acted as a capping agent in the synthesis of silver nanoparticles. The bioreduction method Ag+ to Ag0 produced a silver nanoparticle colloid in brown color. The results of the UV-Vis spectrophotometer showed the silver nanoparticles colloids spectrum at a wavelength of 420 nm with an absorbance value of 0.5. FTIR shows the reduction and shift of absorption peak in the hydroxyl functional group (-OH) at wavenumbers of 3323 cm-1 and the presence of absorption peaks at 560 cm-1. While, XRD pattern showed the specific crystallinity peaks of silver nanoparticles at 2θ: 33.24°; 39.98°; 61.23°; dan 79.13° respectively with the face-centered cubic crystal structure (FCC) and crystallite size of 15 nm. PSA analysis showed two specific peaks with an average size distribution silver nanoparticles of 43.5 nm and a PDI value of 0.4. Analysis of TEM shows the average particle size of 20 nm with a spherical particle shape.

Biosynthesis of silver nanoparticles using citrus sinensis peel extract and their application as antibacterial agent

Silver nanoparticles (Ag-NPs) have attracted huge importance due to their distinctive chemical, biological and physical properties. Silver nanoparticles are widely synthesized by the chemical method, which involves the use of toxic chemicals which affects its applications. The bio-reduction method, in comparison with chemical method is more economic and eco-friendly. In the present work, the bio-based production of Ag-NPs was done by using peel extract of orange (citrus sinensis), which played a role of reducing and stabilizing agent. The biosynthesis of silver nanoparticles was optimized by one factor at a time (OFAT) with respect to peel extract concentration, silver nitrate concentration and reaction temperature. The green synthesized silver nanoparticles were characterized by UV-visible spectroscopy, Fourier transforms infrared (FT-IR) spectroscopy, Scanning electron microscopy (SEM) and X-ray diffraction (XRD). Disk diffusion method was used for the study of antibacterial activity of the bio-synthesized silver nanoparticles against the bacteria Escherichia coli and Staphylococcus aureus. The results showed that at a peel extract concentration of 6%, the temperature of 60oC and silver nitrate concentration of 0.1M, the synthesis of Ag-NPs was effective. The orange peel synthesized Ag-NPs showed effective antibacterial activity against both bacteria. However better activity was observed against bacterium Staphylococcus aureus. The results confirmed the synthesis of Ag-NPs using peel extract of citrus sinensis and its role as antibacterial agent.

Corrigendum to Nanocomposite cellulose fabrics with in situ generated silver nanoparticles by bioreduction method

Corrigendum to Nanocomposite cellulose fabrics with in situ generated silver nanoparticles by bioreduction method

Nanocomposite cellulose fabrics with in situ generated silver nanoparticles by bioreduction method

In the present work, nanocomposite cellulose fabrics with in situ generated silver nanoparticles were prepared by bioreduction method employing aqueous dispersion of low-cost natural turmeric powder as a reducing agent and different concentrated aqueous AgNO3 as source solutions. The prepared nanocomposite cellulose fabrics were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and antibacterial tests. The nanocomposite cellulose fabrics had roughly spherical silver nanoparticles in the size range of 41–130 nm with an overall average of 78 nm. The X-ray analysis indicated the generation of both silver nanoparticles and Ag2O nanoparticles in the nanocomposite cellulose fabrics. The nanocomposite cellulose fabrics retained the generated AgNPs even after repeated detergent washings. The prepared nanocomposite cellulose fabrics exhibited excellent antibacterial activity against both the Gram-negative and Gram-positive bacteria and hence can be considered as antibacterial hospital-bed materials, apparels, etc.

Acclimated growth and characterization of manganese oxide nanospheres using natural extract from trigonella foenum-graecum

ABSTRACT Conventional fabrication of metal Nanoparticles results with a huge price tag and is hazardous to the environment. Hence “Green Technologies” is preferred. This work exhibits modest and bio-friendly fabrication methods of Manganese Oxide (MnO) nanoparticles (NPs) with Trigonella Foenum-Graecum (TFG) commonly known as Fenugreek. The extract prepared from fenugreek seeds acts as both reducing as well as capping agent. The work also exhibits an in-depth comparative study on the Hydrothermal method and Bio-reduction method of synthesis on MnO nanoparticles using fenugreek seeds. The structural and morphological characterizations have been done using SEM, X-Ray Diffraction, TEM and compound formation by FTIR, EDX. UV-Vis spectroscopy exhibits two different band gaps for two different methods of synthesis. The Drug release percentage of both the samples with different concentrations and pH were examined and calculated. The study demonstrates that Manganese Oxide nanoparticle formed from Fenugreek seeds by hydrothermal method and Bio-reduction method.

Ultrasonically driven green synthesis of palladium nanoparticles by Coleus amboinicus for catalytic reduction and Suzuki-Miyaura reaction

A novel ultrasonically driven bio-reduction method was adopted to reduce the palladium chloride into palladium nanoparticles (PdNPs@CA) using coleus amboinicus extract as a green synthetic protocol. XRD confirms the formation of phase pure cubic Pd nanoparticles with the crystallite size range of 40−50 nm. The UV–vis spectrum reveals the formation of Pd nanoparticles by the disappeared peak at 480 nm of PdCl2 solution. The size distribution and surface morphology of prepared Pd nanoparticles showed spherical shaped nanoparticles with less agglomeration. The catalytic reduction behaviour of the Pd suspension is studied by 4-nitro phenol reduction process in 8 min further confirms its high catalytic performance. Synthesized PdNPs@CA were explored in ultrasound promoted Suzuki-Miyaura coupling reaction to determine the catalytic behaviour with ultrasonic frequency of 40 kHz and power of 150 W (Power sonic 410 bath sonicator) and its recycling ability is determined. It was found that aryl halides reacted with aryl boronic acids to obtain biaryl compound with excellent reaction yields in the presence of PdNPs@CA only in 30 min using PEG-400 as a green solvent. PdNPs@CA can be recovered efficiently and reused for 7 cycles without loss of its catalytic property.

In situ generation of silver and silver oxide nanoparticles on cotton fabrics using Tinospora cordifolia as bio reductant

A simple, low cost and environmentally bioreduction method was adopted to in situ generate silver nanoparticles (AgNPs) on the surface of cellulose cotton fabrics utilizing Tinospora cordifolia leaf extract as reducing agent. The bio generation of AgNPs in nanocomposite cellulose cotton fabrics (NCCFs) was confirmed by Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy along with Energy Dispersive X-ray (EDX) spectroscopy, X-ray Diffraction (XRD), primary and derivative thermogravimetric (TG and DTG) analysis and Differential Scanning Calorimetry (DSC). The generated AgNPs in NCCFs were found to be spherical in shape with an average size of 90 nm. The presence of silver element was revealed by EDX spectra with an energy absorption peak at 3 keV. The bio synthesized AgNPs were found to be crystalline in nature from XRD. The bio generated AgNPs in NCCFs were found to be stable up to 399 °C as confirmed by DTG and DSC analysis. These NCCFs also exhibited good mechanical properties. Further, these also exhibited good antibacterial activity against pathogenic disease producing Gram positive (G+ve) and Gram negative (G−ve) bacteria. Basing on these properties, the prepared NCCFs can be considered for medical applications such as hospital bed materials, aprons etc. and also for packing applications.

Sintesis Nanopartikel Perak dan Pengaruh Penambahan Asam p-Kumarat Untuk Aplikasi Deteksi Melamin

Biosynthesis of silver nanoparticles (AgNPs) using mangosteen bark extract, modification and its application in detecting melamine has conducted. This research aimed to synthesize AgNPs via bio-reduction method using mangosteen bark extract followed by modification with p-coumaric acid (APK), and evaluating its application detecting melamine. The AgNPs were characterized through ultraviolet-visible absorption spectroscopy (UV-Vis), Fourier transform infrared absorption spectroscopy (FTIR), and X-ray diffraction (XRD). Observation suggested that an increase of incubation time had affected its surface Plasmon resonance trend. Observation of functional group by FTIR showed that carbonyl group (1707 cm-1) suspected from hydroxyl group (3414 cm-1). Further analysis of crystallite via XRD suggested that nanoparticle size at 30 nm estimated using Debye-Scherer, within the form of unit cells is cubic. Modified AgNPs showed an interaction between APK and particle surface through C=C alkenes (1598 cm-1) and aromatics (1672 cm-1), =C-H aromatic (3070 cm-1), aliphatic C-H (2501 cm-1), C-O (1107 cm-1) and C=O carboxylate (1774 cm-1). The performance of product as melamine detector suggested that the AgNPs-APK had detected melamine in range of concentration from 0.1 to 1000 ppm.

Sintesis Nanopartikel Perak dan Pengaruh Penambahan Asam p-Kumarat Untuk Aplikasi Deteksi Melamin

Biosynthesis of silver nanoparticles (AgNPs) using mangosteen bark extract, modification and its application in detecting melamine has conducted. This research aimed to synthesize AgNPs via bio-reduction method using mangosteen bark extract followed by modification with p-coumaric acid (APK), and evaluating its application detecting melamine. The AgNPs were characterized through ultraviolet-visible absorption spectroscopy (UV-Vis), Fourier transform infrared absorption spectroscopy (FTIR), and X-ray diffraction (XRD). Observation suggested that an increase of incubation time had affected its surface Plasmon resonance trend. Observation of functional group by FTIR showed that carbonyl group (1707 cm-1) suspected from hydroxyl group (3414 cm-1). Further analysis of crystallite via XRD suggested that nanoparticle size at 30 nm estimated using Debye-Scherer, within the form of unit cells is cubic. Modified AgNPs showed an interaction between APK and particle surface through C=C alkenes (1598 cm-1) and aromatics (1672 cm-1), =C-H aromatic (3070 cm-1), aliphatic C-H (2501 cm-1), C-O (1107 cm-1) and C=O carboxylate (1774 cm-1). The performance of product as melamine detector suggested that the AgNPs-APK had detected melamine in range of concentration from 0.1 to 1000 ppm.

Ag impregnated sub-micrometer crystalline jute cellulose particles: Catalytic and antibacterial properties

This work discussed the preparation of Ag nanoparticles (AgNPs) and AgNPs impregnated sub-micrometer crystalline jute cellulose (SCJC) particles using a green synthetic bioreduction method. The ultimate nanocomposite particles were named as SCJC/Ag. The crystalline structure of AgNPs was maintained in SCJC/Ag nanocomposte particles. The catalytic efficiency of SCJC/Ag nanocomposite particles were evaluated for the degradation of congo red (CR) and methylene blue (MB) using NaBH4 as reducing agent. A complete degradation of 20 mL of each CR (0.1 mM) and MB (0.05 mM) dye solution was achieved within 14 min when 0.005 mg mL−1 of SCJC/Ag nanocomposite particles was employed. SCJC/Ag nanocomposite particles also exhibited moderate antibacterial activities against Staphylococcus aureus, Escherichia coli, Shigella dysenteriae and Shigella boydii and the results were comparable with those of the reference AgNPs. SCJC/Ag nanocomposite particles were the most effective against Escherichia coli (E. coli) with minimum inhibitory concentration of 0.014 mg mL-1.

Optimization of synthesis parameters of silver nanoparticles and its antimicrobial activity

Silver nanoparticles (AgNPs) are known today for its antimicrobial activity. It can be synthesized by chemical as well as bio-reduction method. Optimum size of AgNPs plays important role in the antimicrobial activity. The synthesis methods have been employed to improve, size and properties of nanoparticles. In present work we report the qualitative as well as quantitative methods for synthesis of AgNPs, using biological method. The synthesis parameters i.e. Plant leaves, Temperature, pH, and concentration which affects the morphology and yields. AgNPs were characterized using UV–Visible spectrophotometer, FT-IR spectroscopy, X-ray diffraction, Scanning electron microscope, Particle size analyzer (CPS). The AgNPs of 12––17 nm and spherical in shape were synthesized using optimized parameters like Hibiscus leaves extract having pH 6 mixed with 5 mM AgNO3 at 70 °C. The antibacterial activity of AgNPs performed against gram positive (Escherichia coli) and gram negative (Staphylococcus aureus) bacteria.

Enhanced photocatalytic activity of biosynthesized Au-Ag/TiO2 catalyst by removing excess anchored biomolecules

A green bioreduction method was used to prepare highly efficient supported TiO2 photocatalysts with bimetallic (Au-Ag) nanoparticles at room temperature using Cinnamomum camphora leaf extract as both the protective agent and reducing agent. The resulted Au-Ag/TiO2 exhibits high photocatalytic activity toward the degradation of organic dyes. It was demonstrated that after some of the biomolecules were removed through ionic-liquid extraction and/or calcinations, the Au-Ag/TiO2 photocatalyst exhibits significantly enhanced catalytic performance toward the degradation of methyl orange compared to the pristine untreated catalyst. As a result, 300 mL of 20 mg/mL methyl orange can be fully degraded in 30 min. These can be explained by the sufficient biomolecules could protect the nanoparticles stay in small size, but excess biomolecules played an unfavorable role in hindering the electron transportation during the catalytic reaction. The low-cost preparation, the high activity, together with the good stability and recyclability make this developed Au-Ag/TiO2 a promising photocatalyst toward the degradation of wastewater.

A novel cold-adapted nitroreductase from Psychrobactersp. ANT206: Heterologous expression, characterization and nitrobenzene reduction capacity

Widely used in multiple industrial processes, nitro-aromatic compounds, especially nitrobenzene, in low temperature environment are considered as heavy pollutants. Among the disposal methods, the bioreduction method has attracted much attention. In this study, a novel cold-adapted nitroreductase gene (psntr) was cloned from Antarctic sea-ice bacteria Psychrobacter sp. ANT206. The psntr gene was 813 bp in length and encoded a protein with flavin mononucleotide (FMN) binding sites. Homology modeling was performed to obtain structural information such as the longer loops and reduced amount of hydrogen bonds, which might be related to the high catalytic efficiency of PsNTR at low temperature. The psntr gene was successfully cloned in cold-shock pCold I vector and transformed to the expression host Escherichia coli (E. coli) BL21 with the induction by isopropyl β-D-thiogalactoside (IPTG) at low temperature (16 °C) for 24 h. The recombinant PsNTR (rPsNTR) was purified using Ni-NTA with the specific activity of 51.59 μmol/min/mg. Interestingly, rPsNTR displayed the highest activity at 25 °C and still maintained 46.9% of the activity at 0 °C. rPsNTR also exhibited the highest activity (136.4%) at 1.0 M NaCl with incredible salt tolerance. The kinetic parameters and substrates specificity analysis demonstrated that rPsNTR could reduce various nitro-aromatic compounds. Moreover, the result of the reduction capability revealed that the recombinant E. coli exhibited a maximum nitrobenzene reduction rate of 3.03 mM/h at 16 °C. These findings revealed that the characteristics of rPsNTR might make it an excellent candidate for the bioreduction of various nitro-aromatic compounds in the low temperature and high-salt wastewater.