Photoreduction Method Research Articles

In situ deposition of Ag/AgCl on the surface of magnetic metal-organic framework nanocomposite and its application for the visible-light photocatalytic degradation of Rhodamine dye.

Herein, NH2-MIL-125(Ti) (NMT) as one of the known stable metal-organic frameworks (MOFs) in aqueous solution was successfully magnetized with CoFe2O4 nanoparticles through the hydrothermal method. The Ag/AgCl as a plasmonic photocatalyst was assembled on the CoFe2O4/NMT (CFNMT) at room temperature by in situ deposition, and photo-reduction methods to improve the photocatalytic activity of CFNMT under LED visible light. The prepared materials were fully characterized by SEM/EDX, TEM, FTIR, XRD, UV-DRS, and VSM analysis. Rhodamin B (RhB) was selected as the pollutant model. The results showed that the Ag/AgCl@CFNMT had super-fast degradation ability of RhB molecule due to the synergetic effect between Ag/AgCl and CFNMT in comparison with NMT and CFNMT. The introduced Ag/AgCl on the surface of CFNMT increased absorption of photons in the visible region and enhanced the transfer and separation of the produced charge on the contact area between Ag/AgCl and CFNMT. Also, after seven times recycling, besides the simple magnetic separation of Ag/AgCl@CFNMT from liquid media, the composite still showed high photodegradation ability (89%).

Enhanced NIR photocatalytic of Ag-RGO@{010}BiVO4/RGO@{110} BiVO4 photocatalysts induced by resonance effect of transverse electric of RGO and transverse magnetic of Ag

Abstract Highly efficient visible-NIR photocatalytic activity of Ag-RGO@{010}BiVO4/RGO@{110}BiVO4 photocatalysts are successfully synthesized via an in situ photoreduction method. The transverse electric TE mode accompanied by surface plasmon collective excitations of RGO compel photocatalyst to absorb NIR light. Significantly, the degradation rate of 15%Ag-RGO@{010}BiVO4/RGO@{110}BiVO4 photocatalysts can reach the highest 98.3% and 66.1%, and the mineralization yield can reach to 97.22% and 74.25% within 90 min under visible and 180 min NIR irradiation, respectively. The extraordinary visible and NIR photocatalytic activity is attributed to resonance effect of local electric field formed by transverse electric TE mode of RGO and local magnetic field formed by transverse magnetic TM of plasmonic Ag can accelerate carrier separation, and energetic carriers induce by SPR effect of plasmonic Ag nanoparticles can directly oxidize organic pollutants to small molecules. The as-synthesized Ag-RGO@{010}BiVO4/RGO@{110}BiVO4 hybrid photocatalysts exhibit excellent wide-spectrum response to wavelengths ranging from visible to near-infrared (NIR), indicating its potential for effective utilization of solar energy.

Ag/AgCl/MIL-101(Fe) Catalyzed Degradation of Methylene Blue under Visible Light Irradation.

A novel photo-Fenton catalyst named Ag/AgCl/MIL-101(Fe) was synthesized by the method of precipitation and photo reduction and characterized by X-ray diffraction patterns (XRD), Brunauer-Emmett-Teller (BET) measurements, Fourier transform infrared spectra (FTIR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectra. Moreover, the catalytic activity of the synthesized catalyst was tested using methylene blue (MB) as the target pollutant. The obtained results illustrated that the plasmonic material Ag/AgCl was successfully loaded on MIL-101(Fe) and the obtained catalyst exhibited an excellent catalytic activity under visible light at the neutral pH. According to the analyses of Plackett-Burman and Box-Behnken design, the optimum conditions for MB degradation were obtained. Under these conditions, the MB decolorization and mineralization efficiencies could reach to 99.75% and 65.43%, respectively. The recycling experiments also showed that the as-prepared catalyst displayed good reusability. In addition, the possible reaction mechanisms for the heterogeneous photo-Fenton system catalyzed by Ag/AgCl/MIL-101(Fe) were derived. The synthesized catalyst provides a promising approach to degrade organic pollutants in waste water.

A green approach for the reduction of graphene oxide by the ultraviolet/sulfite process

This study highlights a green approach for the reduction of graphene oxide (GO) using the ultraviolet/sulfite advanced reduction process (UV/sulfite process). X-ray photoelectron spectroscopy (XPS) provided a strong evidence on the efficient reduction of GO by increasing the C/O ratio from 2.0 to 4.8, and the successful reduction was also characterized by UV–Vis, XRD and Raman spectrometry. The reduction of GO was attributed to the hydrated electrons generated from both sulfite photolysis (major, contributed by 71.4%) and GO photolysis (minor, contributed by 21.6%) under UV irradiation. The dissolved oxygen in water exhibited inhibitory effect on GO reduction through scavenging of the hydrated electrons. Moreover, the reduction efficiency of GO decreased with the increasing UV wavelength from 254 nm to 365 nm, because of the reduced molar absorptivity of sulfite at higher UV wavelength. By using this green photo-reduction method, high-purity of reduced graphene oxide can be easily obtained by water-rinse, since soluble sulfite are the only by-products. In conclusion, the research outcomes provide mechanistic insights on the GO reduction by the hydrated electron-based advanced reduction processes, which has great potential for the environmental-friendly and cost-effective reduction of GO.

Synthesis and characterization of aminolevulinic acid with gold and iron nanoparticles by photoreduction method for non-communicable diseases diagnosis and therapy

Non-communicable diseases (NCDs) are a group of chronic diseases resulted by genetic, epigenetic and environmental factors and life style. The main types of NCDs are cardiovascular diseases and cancers. Some of therapeutic treatments for NCDs induce severe cytotoxicity to normal cells. New treatments as photodynamic and sonodynamic therapies have been proposed trying to improve the cure rate and reduce the side-effects. In these treatments certain drugs as porphyrins precursors associated to metal nanoparticles (MNPs) have become of extreme interest since have high targeting ability and potentiality to destroy tumor tissues. MNPs can induce cell death through various processes, including reactive oxygen species (ROS) generation and DNA damage, among others. In this work, we describe synthesis of MNPs by photoreduction with aminolevulinic acid (ALA), a protoporphyrin IX precursor. To obtain ALA:MNPs (M = Au or/and Fe), ALA, polyethylene glycol, and Tetrachloroauric acid and/or iron powder water solutions were irradiated by Xenon lamp. The UV–vis spectra, transmission electron microscopy and zeta potential were measured to characterize nanoparticles. The proposed mechanism of nanoparticle formation was described from a physicochemical perspective. The THP-1 macrophages cytotoxicity was determined, and photodynamic therapy (PDT) with high power LED at 590 nm for 2 min were performed. The results have suggested that the gold/iron nanoparticles interfere in the selectivity of iron transport across the mitochondrial inner membrane and enhance the effectiveness of the PDT acting as important agent for NCDs control.

Separation of Re(VII) from aqueous solution by acetone-enhanced photoreduction: an insight into the role of acetone

Efficient separation of rhenium (Re) from aqueous solution is pivotal in the resource recovery, and suitable to simulate the elimination of radiotoxic technetium (Tc) due to their similar properties. In this work, we achieved a high Re(VII) separation ratio of 95.2% within 30 min from aqueous solution via an acetone-enhanced photoreduction method, in which soluble ReO4− was reduced to insoluble ReOx and Re(0) in the presence of acetone and isopropanol. Compared with the situation in absence of acetone, acetone absorbed most of the UV energy, and the produced triplet acetone could abstract Hα atoms from isopropanol to form more strongly reductive ketyl radicals, leading to the enhancement in photoreduction. Isopropanol was the most qualified for Re(VII) photoredction due to its low C–Hα bond energy. The addition of alkali also benefited the Re(VII) separation by eliminating produced protons, and stabilizing the intermediate Re(VI) to preventing the re-formation of Re(VII) through disproportionation of Re(VI). Furthermore, selective and effective separation of Re(VII) from simulated high level liquid waste containg Nd(III) was realized as well. This work gains an insight into the role of acetone in the enhanced Re(VII) photoreduction, which may be of great significance in developing novel approaches for hydrometallurgy and spent nuclear fuel reprocessing.

Enhanced photocatalytic property of Ag loaded on well-defined ferroelectric Na3VO2B6O11 crystals under visible light irradiation

How to efficiently utilize visible light and highly separate photo-induced charges is now a hot topic in the field of photocatalysis. Herein, various amounts (1–5%, wt%) of Ag nanoparticles were selectively deposited on the surface of the polar material Na3VO2B6O11 (NVB) via the method of photoreduction. Due to the presence of external screening effect, the Ag nanoparticles were selectively deposited on the positive domains of NVB materials. Through DFT, the (110) facet with excessive electrons accumulated has a high reduction ability to deposit the Ag nanoparticles on the edge of NVB crystals. It was also found that the surface plasmon resonances effect of Ag nanoparticles led to the absorption spectrum of NVB broadened to the visible range around 400–800 nm. Under visible light irradiation, the photodegradation efficiency of NVB was significantly enhanced with the 4% Ag deposition, which reached 96% for 2-Chlorophenol (2-CP) degradation in 100 min. It indicates that the screening effect of NVB combination with the surface plasmon resonances effect from Ag nanoparticles can provide a synergistic effect on the enhanced photocatalytic activity during the 2-CP degradation.

Enhanced hydrogen evolution from CuOx-C/TiO2 with multiple electron transport pathways.

Titanium dioxide nanoparticles co-modified with CuOx (0≤x≤2) and carbonaceous materials were prepared with a simple hydrolysis and photo-reduction method for photocatalytic hydrogen generation. SEM/TEM and XPS analysis indicated that the carbonaceous materials were mostly coated on the TiO2 surface and clearly revealed that the Cu species exhibited multivalence states, existing as CuOx (0≤x≤2). The optimal catalyst showed a 56-fold enhanced hydrogen evolution rate compared with that of the pure C/TiO2 catalyst. Further, an intensive multiple electron transfer effect originating from CuOx and the carbonaceous materials is proposed to be responsible for the elevated photoactivity. CuOx species serve as electron donors facilitating charge carrier transfer and proton reduction sites. The carbonaceous materials function as the “bridge” that transfers the electrons of TiO2 to the CuOx species, which provides a new route for electron transfer and reinforces the effect of CuOx as a co-catalyst. In this study, the CuOx and C co-modified TiO2 catalyst was prepared with multiple electron transport pathways and enhanced hydrogen production evolution, which provides a deep understanding for the design of co-catalyst-based photocatalysts.

Photocatalytic one-step synthesis of Ag nanoparticles without reducing agent and their catalytic redox performance supported on carbon

Synthesis of silver nanoparticles (Ag NPs) with state-of-the-art chemical or photo-reduction methods generally takes several steps and requires both reducing agents and stabilizers to obtain NPs with narrow size distribution. Herein, we report a novel method to synthesize Ag NPs rapidly in one step, achieving typical particle sizes in the range from 5 to 15 nm. The synthesis steps only involve three chemicals without any reducing agent: AgNO3 as precursor, polyvinylpyrrolidone (PVP) as stabilizer, and AgCl as photocatalyst. The Ag NPs were supported on carbon and showed excellent performance in thermal catalytic p-nitrophenol reduction and nitrobenzene hydrogenation, and as electrocatalyst for the oxygen reduction reaction.

Improving hydrogen evolution activity of perovskite BaTiO3 with Mo doping: Experiments and first-principles analysis

Hydrogen production through photocatalytic water splitting attracts great attention in fields of energy conversion. To improve the hydrogen evolution efficiency, narrowing the bandgap of photocatalysts by introducing dopant atoms is widely investigated for increasing light absorption. Herein, Mo-doped BaTiO3 samples are synthesized by a traditional solid-state reaction method and all the samples are modified with Pt by a photo-reduction method. Compared with pure BaTiO3, Mo doping into BaTiO3 samples realizes the band-to-band visible-light absorption and shows remarkable improvement in hydrogen production efficiency. Under simulated sunlight irradiation and with 0.4 wt% Pt deposition, BaTiO3 doped with 2 at% Mo exhibits a hydrogen evolution rate of 63 μmol g−1 h−1, about 2 times improvement in comparison to pure BaTiO3 (35 μmol g−1 h−1). Further first-principles calculations based on density-function theory demonstrates an apparent downward movement of the conduction band minimum due to the coupling between the Ti 3d and Mo 3d states, leading to the significant bandgap narrowing and enhancement of the visible-light photocatalytic activity.

Microwave induced surface enhanced pollutant adsorption and photocatalytic degradation on Ag/TiO2

In this work, Ag/TiO2 composite was prepared by photo-reduction method. The study of photocatalytic degradation of different organic pollutants found that microwave can enhance the photocatalytic degradation rate. Further studies have shown that photo-generated holes are the main active species involved in photocatalytic degradation. Under microwave irradiation, silver nanoparticles can not only promote the charge separation process, but also enhance the adsorption of organic pollutants on the surface of TiO2.

Au-decorated 3D/1D titanium dioxide flower-like/rod bilayers for photoelectrochemical water oxidation

Photoelectrochemical water splitting can be regarded as a promising technology for renewable hydrogen production. In the current work, a facile hydrothermal synthesis method was used to directly grow TiO2 flower-like structures/TiO2 nanorods on a conductive glass substrate. Moreover, three different gold deposition methods, namely, a photoreduction method (PR), the Turkevich method (TK) and a combination of both methods (CM), were applied to decorate the formed flower-like structures with gold nanoparticles (GNPs). The type of deposition technique affected the size, size distribution, loading, surface coverage and shape of the obtained GNPs. With the PR technique, the photocurrent increased 3.5-fold compared to that of the bare flower-like structures. With the TK method, a narrow GNP distribution was obtained, yielding a 6.15-fold increase in photocurrent. Using the CM approach, a 1.21-, 26.86- and 12.79-fold increase was observed for current density compared to that of the corresponding bare samples. All samples showed stable chronoamperometric performance under illumination without any signs of photocorrosion or performance deterioration. Electrochemical impedance spectroscopy showed that the CM approach decreased the semiconductor/electrolyte interfacial resistance to 37, 2.5 and 3.1% of the values for the bare samples. Bode phase plots showed that the stacked flower-like structures can be considered electron-hole recombination centres, leading to an observable broadening of the maximum-frequency peak.

Z-scheme structure SnS2–Au–CdS with excellent photocatalytic performance for simultaneous removal of Cr(VI) and methyl orange

A highly efficient Z-scheme photocatalyst SnS2–Au–CdS was fabricated by photoreduction and thiourea medium deposition methods. It was found that Au nanoparticles were successfully anchored on the surface of SnS2, and CdS nanoparticles were further deposited on the surface Au nanoparticles by the strong interaction of S–Au. Compared to SnS2, CdS, SnS2–Au, and SnS2–CdS, Z-scheme structure SnS2–Au–CdS shows the best photocatalytic performance for methyl orange (MO) degradation and Cr(VI) reduction under visible light irradiation. The outstanding photocatalytic performance of SnS2–Au–CdS can be ascribed to the special Z-scheme structure which not only improves the separation of photogenerated charge carriers but also preserves its high redox ability. In addition, SnS2–Au–CdS exhibited synergistic effects in photocatalytic removal of Cr(VI) and MO.

Effect of surface Ag metallization on the photocatalytic properties of BaTiO3: Surface plasmon effect and variation in the Schottky barrier height

Surface Ag metallized BaTiO3 samples were prepared by varying Ag concentration in the range of 0.2% to 0.8% by photoreduction method and the performance of these catalysts were tested for the degradation of Rhodamine B dye under the illumination of UV/solar light. The values of lattice parameter, cell volume and lattice strain has increased with increase in the Ag concentration, while the crystallite size decreased with increase in the deposited Ag concentration. The surface plasmon absorption bands of Ag deposited BTO samples showed a red-shift and the absorption bands broadened with increase in the Ag content. The presence of surface metallic silver in the Ag0 state was confirmed by the XPS analysis. The enhanced activity of Ag deposited photocatalyst under UV light is majorly due to the formation of Schottky barrier, creation of metal induced gap states, polarization effects, reduced crystallite size and increased surface area of the photocatalyst. Under solar light it is due to synergistic effects between Surface Plasmon Resonance (SPR) effect and formation of Schottky barriers. The photocurrent measurements substantiates the effective charge transfer migrations. The energy states/term symbols of the metallic Ag under the illumination of UV light is 2S1/2 and it is 2P1/2 under the illumination of solar light.

Light-induced confined growth of amorphous Co doped MoSx nanodots on TiO2 nanoparticles for efficient and stable in situ photocatalytic H2 evolution

Amorphous molybdenum sulfide (a-MoSx) prepared by in situ photoreduction method with an abundance of exposed active sites has been identified as an efficient cocatalyst for catalyzing photocatalytic H2 evolution reaction (HER). However, the intrinsic activity of the a-MoSx cocatalyst toward HER is low due to the unfavorable electronic structures of the active sites. Herein, we report a facile light-induced method for the confined growth of transition metal (TM) doped MoSx (a-TM-MoSx) cocatalysts on TiO2 nanoparticles and their catalytic activity for in situ photocatalytic HER. It is found that doping Co into a-MoSx can greatly enhance the activity of resulted a-Co-MoSx cocatalyst for photocatalytic H2 evolution over TiO2 among the transition metal dopants (Co, Ni, Fe, Cu, Zn) tested. The most efficient a-Co-MoSx cocatalyst (Co/Mo = 1/4 and 4 mol% loading) loaded TiO2 (TiO2/a-Co-MoSx) shows a H2 evolution rate of 133.8 μmol h−1, which is 3.3 times higher than that of a-MoSx loaded TiO2 (TiO2/a-MoSx). Moreover, the TiO2/a-Co-MoSx photocatalyst shows excellent recycling H2 evolution stability. The characterization results reveal that a-Co-MoSx cocatalyst can not only effectively capture the photogenerated electrons of TiO2 to greatly enhance the separation efficiency of photogenerated charges but also significantly reduce the overpotential of HER due to the formation of highly active “CoMoS” sites, thus synergistically enhancing the catalytic activity of TiO2/a-Co-MoSx. Moreover, the light-induced growth of a-Co-MoSx on TiO2 is found to readily couple with the in situ photocatalytic HER. Therefore, this work provides a simple and efficient strategy for designing high-performance a-MoSx-based cocatalysts for stable in situ photocatalytic H2 evolution.

Facile synthesis of Ag Bi25GaO39Bi2WO6 heterostructure with enhanced photocatalytic performance based on interface structure design

Abstract Composite photocatalytic system based on interface structure design is deemed to be a feasible method to improve the photocatalytic efficiency of sillenite-type photocatalytic material. Therefore, we reported the successful construction of novel tetrahedron-like Ag Bi25GaO39 Bi2WO6 heterostructure through a partial chemical conversion strategy coupling with the photo-reduction method. Experiment indicated that the as-prepared Ag Bi25GaO39 Bi2WO6 heterogeneous structure possessed excellent photo-degradation activity for the decomposition of Rhodamine B (RhB) and 95% of RhB molecules could be decomposed after 20 min of UV–vis light irradiation by comparison of single Bi25GaO39 and Bi2WO6, as well as the Bi25GaO39 Bi2WO6 heterostructure. Moreover, the resulted Ag Bi25GaO39 Bi2WO6 product also exhibited outstanding photocatalytic activity for the decomposition of other pollutant such as phenol and toxic Cr(VI) solutions. Due to the resulted advantages derived from the rational design of interface structure (matching band structure, intimate interfacial contacts, “face-to-face” contact mode of hetero-interface and the famous “schottky barriers), the photo-generated charges generated in the composite photocatalytic system could be separated quickly, thus exhibiting excellent photocatalytic ability. This design concept can provide new ideas for the construction of other similar composite photocatalytic systems.

Enhancement in photocatalytic performance of Ag–AgCl decorated with h-WO3 and mechanism insight

A h-WO3 decorated Ag–AgCl composite was prepared through facile precipitation and photoreduction methods and demonstrated to be a highly efficient and stable photocatalyst for the degradation of Rhodamine B (RhB) under visible light. Ag–AgCl/h-WO3 exhibited much improved photocatalytic performance was elucidated from the physical–chemical properties of AgCl and h-WO3 and the surface plasmon resonance effect of the Ag particles. The techniques of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectrometry (XPS) and photocurrent were used to characterize crystalline phases, morphology, composition and separation efficiency between electrons (e−) and holes (h+) of the synthesized composite photocatalyst. XPS results confirmed the existence of W5+ and W6+ on the surface of h-WO3 sample, which favored electrons transfer between AgCl and Ag, and generated superoxide radical for the degradation of RhB. The active species trapping experiments results further demonstrated that the formation of superoxide radical during the system. Finally, the underlying photocatalytic mechanism for the removal of RhB by Ag–AgCl/h-WO3 composite was examined.

Tryptophan Silver Nanoparticles Synthesized by Photoreduction Method: Characterization and Determination of Bactericidal and Anti-Biofilm Activities on Resistant and Susceptible Bacteria.

The high rates of antibiotics use in hospitals have resulted in a condition where multidrug-resistant pathogens have become a severe threat to the human health worldwide. Therefore, there is an increasing necessity to identify new antimicrobial agents that can inhibit the multidrug-resistant bacteria and biofilm formation. In this study, antibacterial and anti-biofilm activities of tryptophan silver nanoparticles (TrpAgNP) were investigated. The TrpAgNPs were synthesized by photoreduction method, and the influence of irradiation time and concentration of reagents were analyzed. The nanoparticles were characterized by transmission electron microscopy, Zeta Potential and (UV)-absorption spectra. The antibacterial activity of TrpAgNPs was tested for antibiotic-resistant and susceptible pathogens, Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Citrobacter freundii, Klebsiella pneumoniae, Salmonella typhimurium, and Pseudomonas aeruginosa, evaluating the influence of photoreduction parameters in bactericidal effect. The results have shown that TrpAgNPs solutions with lower tryptophan/silver nitrate (AgNO3) ratio and higher AgNO3 concentration have higher bactericidal action against bacteria with inhibition of ~100% in almost all studied bacterial strains. The antimicrobial activity of TrpAgNPs within biofilms generated under static conditions of antibiotic-resistant and susceptible strains of S. aureus, S. epidermidis, E. coli, K. pneumoniae, C. freundii, and P. aeruginosa was also investigated. The results showed that TrpAgNPs have an inhibitory effect against biofilm formation, exceeding 50% in the case of Gram-negative bacteria (E. coli, K. pneumoniae, C. freundii, and P. aeruginosa—54.8% to 98.8%). For Gram-positive species, an inhibition of biofilm formation of 68.7% to 72.2 % was observed for S. aureus and 20.0% to 40.2% for S. epidermidis.

Broadband photocatalysis using a Z-scheme heterojunction of Au/NaYF4:Yb,Er/WO3·0.33H2O-W18O49via a synergetic strategy of upconversion function and plasmonic effect

Employing upconversion hosts and plasmonic Au, this work deals with the synthesis of a novel heterojunction via a hydrothermal followed by a photo-reduction method.

Effects of the preparation method of Pt/g-C3N4 photocatalysts on their efficiency for visible-light hydrogen production.

As a two-dimensional (2D) nanomaterial, bulk g-C3N4 (CNB) has a low specific surface area and weak electron transport ability, which limit its application in photocatalysis. In this paper, ultrathin porous g-C3N4 nanosheets (CNS) have been synthesized by thermal oxidation etching of CNB. Compared with CNB, CNS possess a larger surface area of 234.65 m2 g-1, good dispersity in water and a high electron transfer rate. As a co-catalyst, ultra-small Pt nanoparticles (NPs) with high dispersity are successfully loaded on the surface of CNS. It is found that changing the loading method of Pt NPs in the preparation step remarkably alters the efficiency for hydrogen production. The Pt/CNS-CR photocatalyst fabricated by the chemical reduction (CR) method shows a much higher efficiency for H2 evolution from water splitting, compared to the Pt/CNS-PR photocatalyst obtained by the loading of Pt NPs by the traditional photo-reduction (PR) method. When triethanolamine (TEOA) is used as a hole sacrificial agent, the hydrogen production rate of 2.0%-Pt/CNS-CR is 7862.5 μmol g-1 h-1, which is 6.92 times higher than that of 2.0%-Pt/CNS-PR (1136.8 μmol g-1 h-1). The valence states of the Pt element in the Pt/CNS-CR and Pt/CNS-PR nanocomposites have been analyzed by X-ray photoelectron spectroscopy, respectively. At the same time, the effects of the loading amount of Pt and different sacrificial reagents on the photocatalytic H2 generation activity have also been systematically investigated.