Photo-assisted Reduction Method Research Articles

Synthesis of silver nanoparticles with long-term storability for SERS applications using aqueous extracts of rice bran: A rapid and green photochemical approach

This study focuses on the green synthesis of silver nanoparticles (AgNPs) using photo-assisted rice bran extract reduction methods with LED irradiation of varying wavelengths. The AgNPs synthesized using this photochemical method (with violet LEDs) have a narrow size distribution of 10 ± 5 nm. The photoreaction is almost complete within 3 min under the irradiation of violet LED arrays (405 nm, 40 mW/cm2). In contrast, almost no AgNPs were formed using a heating reaction at 90 °C for 3 h. The light conversion efficiency of the photo-assisted reduction method using rice bran extract is over 6 times better than using citrate ions. We propose that the organic acids in rice bran extract are acting as efficient photo-reduction reagents that reduce silver ions to generate AgNPs. The proteins with thiol groups in the rice bran extract act as capping agents, confining the sizes of AgNPs and preventing AgNPs from aggregation through the formation of Ag-S bonds. The excitation wavelength-dependent experiments show that the threshold of photon-energy for photo-assisted rice bran extract reduction is about 2.3 eV. We also found that most of the as-prepared AgNPs retain their morphologies and are well-dispersed for at least 2 months. This photo-assisted rice bran extract reduction method is an easy, fast, green, and highly reproducible process to synthesize stable AgNP colloids for SERS applications.

Plasmonic Ag/AgCl/NH2-MIL-88B (Fe) inorganic-organic hybridized heterojunction as visible-light-driven photocatalyst for hexavalent chromium reduction

To effectively photocatalytic removal of Cr (VI), this work focuses on constructing the inorganic-organic hybridized heterojunction composite photocatalyst of Ag/AgCl/NH2-MIL-88B (Fe), where the Ag/AgCl nanoparticles were deposited on the surface of mesoporous NH2-MIL-88B (Fe) via a simple photo-assisted reduction method. The formation of the ternary Ag/AgCl/NH2-MIL-88B (Fe) composite presented more stable and higher photocatalytic reduction performance for Cr (VI) removal than that of MIL-88B (Fe) photocatalyst. Its photo-reduction rate reached to 85.7%, which was ascribed to its high separation and migration efficiency of photogenerated electrons and holes pair. The formed heterojunction structure and surface plasmon resonance effect originated from Ag/AgCl could largely enhance the absorption capacity of visible light, which promotes the excitation of photogenerated electrons, accelerates their transfer, and reduces the recombination rate of electrons and holes. Besides, a possible catalytic mechanism of this reaction is proposed by the photo-induced charge transfer path in the Ag/AgCl/NH2-MIL-88B (Fe) inorganic-organic hybridized system.

Enhanced visible-light-induced photocatalytic degradation and disinfection activities of oxidized porous g-C3N4 by loading Ag nanoparticles

Herein, Ag nanoparticles (AgNPs) were loaded on oxidized porous g-C3N4 (PCNO) via photo-assisted reduction method. Compared with PCNO, Ag/PCNO plasmonic photocatalysts possessed remarkably enhanced photocatalytic performances in both pollutant degradation and disinfection under visible light irradiation. The optimum photocatalytic activity of Ag/PCNO at a loading amount of 2.0 wt% (Ag-2/PCNO) on amaranth degradation was almost 2.4 times as fast as that of PCNO. Additionally, Ag-2/PCNO could inactivate about 99.4% of Staphylococcus aureus (S. aureus) cells after 3 h of irradiation, whereas only about 29.6% of S. aureus cells were inactivated by PCNO. The enhancement of photocatalytic activities for Ag/PCNO composites could be ascribed to the combination of the SPR effect of AgNPs and the synergistic effect from PCNO molecules, which resulted in enhanced absorption in visible-light region, improved charge transfer, and reduced charge recombination. Moreover, h+ and O2− were the dominate reactive species for Ag/PCNO composites to remove azo pigments and pathogenic bacteria efficiently during the photocatalytic process.

Designing non-noble/semiconductor Bi/BiVO4 photoelectrode for the enhanced photoelectrochemical performance

Bi/BiVO4 photoelectrode was prepared on FTO glass by the combination of electrochemical deposition, heating treatment and photo-assisted reduction method at room temperature. All of the samples were characterized by X-ray diffraction spectrum (XRD), scanning electron microscope (SEM) and UV–vis diffuse reflectance spectrum (DRS), respectively. The results indicated that metallic Bi particles were well deposited on porous BiVO4 film during the deposition process of photo-assisted reduction, resulting in a greatly broadened visible light absorption edge than that of BiVO4 alone. The optimized photoelectrochemical (PEC) performance of Bi/BiVO4-60 was further verified by linear scan voltammetry (LSV), current-time (I-t) and incident photon-to-current efficiency (IPCE), respectively. It was conjectured the broadened visible light response range of Bi/BiVO4 PEC system and the increased counteraction against positive charge both were caused by the electron transferred from BiVO4 to Bi, and thus effectively facilitated the separation and transfer of photo-generated carriers and thus promote the PEC water splitting performance.

Enhancement of photocatalytic and photoelectrocatalytic activity of Ag modified Mpg-C3N4 composites

In this study, mpg-C3N4/Ag composites of surface plasmon resonance structures were fabricated to improve the photocatalytic and photoelectrocatalytic activities of g-C3N4 via photo-assisted reduction method, which were characterized by XRD, EDS, XPS, FT-IR, FE-SEM, TEM, DRS and BET. The photocatalytic and photoelectrocatalytic activities were evaluated by the degradation of methylene blue (MB) and the oxygen reduction experiment under visible light. The results showed the photocatalytic and photoelectrocatalytic activities were dependent on the weight ratio of Ag and the optimum photocatalytic activity of mpg-C3N4/Ag at a weight ratio of 3% is almost 3 times as high as that of mpg-C3N4. Additionally, mpg-C3N4/Ag exhibited a significantly enhanced oxygen reduction performance under visible light. The limit current density was increased about 2 times by the modification of Ag nanoparticles, compared with that of pristine mpg-C3N4. Finally, based on the first principle, the enhancement mechanism of the photocatalytic and photoelectrocatalytic activities was discussed by the calculation on the band structure and density of states in the mpg-C3N4/Ag composites. The appropriate amount of Ag modification would cause the surface plasmon resonance effect, which improved the photocatalytic, photoelectrocatalytic, and oxygen reduction activities of mpg-C3N4.

Enhanced disinfection application of Ag-modified g-C3N4 composite under visible light

Ag/g-C3N4 composite photocatalyst, which was synthesized by thermal polymerization of melamine precursor combined with the photo-assisted reduction method, was applied as an efficient visible-light-driven photocatalyst for inactivating Escherichia coli (E. coli). The composite photocatalysts exhibited significantly enhanced photocatalytic disinfection efficiency than pure g-C3N4 powders. The mechanism of enhanced disinfection activity was systematically investigated by UV–visible diffuse reflectance spectra, photoluminescence spectra, and photo-electrochemical methods including photogenerated current densities, electrochemical impedance spectroscopy (EIS) spectra and Mott–Schottky plots. The enhanced photocatalytic bactericidal effect was attributed to the hybrid effect from Ag and g-C3N4, which resulted in enhanced adsorption of visible light, reduced recombination of free charges, rapid separation and transportation of photogenerated electrons–holes. The disinfection mechanism was studied by employing chemical scavengers and ESR technology, indicating the important role of h+ and e−. Considering the bulk availability and excellent disinfection activity of Ag/g-C3N4, it is a promising solar-driven photocatalyst for cleaning microbial contaminated water in practice.

Silver-functionalized g-C3N4 nanohybrids as signal-transduction tags for electrochemical immunoassay of human carbohydrate antigen 19-9.

A simple and feasible electrochemical immunosensing platform was developed for highly efficient screening of a disease-related protein (human carbohydrate antigen 19-9, CA 19-9 used in this case) using silver-functionalized g-C3N4 nanosheets (Ag/g-C3N4) as signal-transduction tags. Initially, Ag/g-C3N4 nanohybrids were synthesized by combining thermal polymerization of the melamine precursor with the photo-assisted reduction method. Thereafter, the as-synthesized Ag/g-C3N4 nanohybrids were utilized for the labeling of the anti-CA 19-9 detection antibody by using a typical carbodiimide coupling method. The assay was carried out on a capture antibody-modified glassy carbon electrode in a sandwich-type detection mode. The detectable signal mainly derived from the voltammetric characteristics of the immobilized nanosilver particles on the g-C3N4 nanosheets within the applied potentials. Under the optimal conditions, the voltammetric peak currents increased with the increasing amount of target CA 19-9, and exhibited a wide linear range from 5.0 mU mL(-1) to 50 U mL(-1) with a detection limit of 1.2 mU mL(-1). Our strategy also displayed good reproducibility, precision and specificity. The results of the analysis of clinical serum specimens were in good accordance with the results obtained by an enzyme-linked immunosorbent assay (ELISA) method. The newly developed immunosensing system is promising for enzyme-free and cost-effective analysis of low-abundance proteins.

Photo-assisted synthesis of Ag3PO4/reduced graphene oxide/Ag heterostructure photocatalyst with enhanced photocatalytic activity and stability under visible light

A novel Ag3PO4/reduced graphene oxide/Ag nanocrystals (Ag3PO4/RGO/Ag) heterostructure photocatalyst has been synthesized using a facile photo-assisted reduction method for the first time. The Ag3PO4/RGO/Ag that consists of close chemical bonding between RGO and Ag3PO4 nanoparticles as well as dispersive plasmonic Ag nanocrystals on the RGO sheets exhibited superior photocatalytic activity and stability to bare Ag3PO4, Ag/Ag3PO4 and Ag3PO4/GO in degradation of Rhodamine B and phenol under visible light. It is suggested that the photo-generated electrons in Ag3PO4 can be transferred to RGO/Ag, leading to efficient separation and transfer of electron–hole pairs. Meanwhile, under light irradiation, the plasmonic Ag nanocrystals also generate electron–hole pairs through surface plasmon resonance (SPR), in which the active electrons can facilitate the formation of additional active species of O2•− for photocatalysis whereas the holes can be filled by electrons from RGO. As a result, both the photocorrosion of Ag3PO4 and the recombination of electron–hole pairs are suppressed due to the special electron transfer route of Ag3PO4→RGO→Ag in the heterostructure. This work suggests that the reasonable combination of semiconductors and graphene decorated with noble metallic nanocrystals can provide a versatile strategy for the synthesis of high efficient heterostructed photocatalysts.

Unique Electrochemical Catalytic Behavior of Pt Nanoparticles Deposited on TiO2 Nanotubes

In this study, we have directly deposited Pt nanoparticles on TiO2 nanotubes (TiO2/Pt) using a facile photoassisted reduction method. The Pt nanoparticles deposited on the TiO2 nanotube arrays possess a large electrochemically active surface area and exhibit remarkable kinetic behaviors. The peaks for the oxide formation and reduction progressively decrease and eventually disappear completely after 800 cycles, whereas the integrated charge for hydrogen adsorption and desorption reaches a constant, ∼70% of the initial value. In addition, an S-shaped cyclic voltammogram observed for the methanol oxidation at the electrochemically treated TiO2/Pt electrode was dramatically different from the results obtained at a bulk Pt electrode. The self-refreshment functionality and anatomy of the reconstructed TiO2-supported Pt nanoparticles described in this study provide a new approach for improving the catalytic activity of Pt nanomaterials in renewable energy applications.

Photo-assisted preparation and patterning of large-area reduced graphene oxide–TiO2 conductive thin film

A mild photo-assisted reduction method was developed to fabricate large-area, uniform reduced graphene oxide-TiO(2) films and micropatterns on various substrates in air at room temperature from a composite insulating film of graphene oxide sheets and TiO(2) nanoparticles, with a conductivity (0.5-2 Omega cm) comparable to chemically reduced graphene.