Sulfur-mediated photodeposition synthesis of NiS cocatalyst for boosting H2-evolution performance of g-C3N4 photocatalyst

Modification of nickel sulfide cocatalysts is considered to be a promising approach for efficient enhancement of the photocatalytic hydrogen production performance of g-C3N4.Providing more NiS cocatalyst to function as active sites of g-C3N4 is still highly desirable.To realize this goal,in this work,a facile sulfur-mediated photodeposition approach was developed.Specifically,photogenerated electrons excited by visible light reduce the S molecules absorbed on g-C3N4 surface to S^2‒,and subsequently NiS cocatalyst is formed in situ on the g-C3N4 surface by a combination of Ni2+and S2‒due to their small solubility product constant(Ksp=3.2×10^‒19).This approach has several advantages.The NiS cocatalyst is clearly in situ deposited on the photogenerated electron transfer sites of g-C3N4,and thus provides more active sites for H2 production.In addition,this method utilizes solar energy with mild reaction conditions at room temperature.Consequently,the synthesized NiS/g-C3N4 photocatalyst achieves excellent hydrogen generation performance with the performance of the optimal sample(244μmol h^‒1 g^‒1)close to that of 1 wt%Pt/g-C3N4(316μmol h^‒1 g^‒1,a well-known excellent photocatalyst).More importantly,the present sulfur-mediated photodeposition route is versatile and facile and can be used to deposit various metal sulfides such as CoSx,CuSx and AgSx on the g-C3N4 surface,and all the resulting metal sulfide-modified g-C3N4 photocatalysts exhibit improved H2-production performance.Our study offers a novel insight for the synthesis of high-efficiency photocatalysts.

Metal-seed assistant photodeposition of platinum over Ta_(3)N_(5) photocatalyst for promoted solar hydrogen production under visible light

Cocatalysts play a vital role in accelerating the reaction kinetics and improving the charge separation of photocatalysts for solar hydrogen production.The promotion of the photocatalytic activity largely relies on the loading approach of the cocatalysts.Herein,we introduce a metal-seed assistant photodeposition approach to load the hydrogen evolution cocatalyst of platinum onto the surface of Ta_(3)N_(5) photocatalyst,which exhibits about 3.6 times of higher photocatalytic proton reduction activity with respect to the corresponding impregnation or photodeposition loading.Based on our characterizations,the increscent contact area of the cocatalyst/semiconductor interface with metal-seed assistant photodeposition method is proposed to be responsible for the promoted charge separation as well as enhanced photocatalytic H2 evolution activity.It is interesting to note that this innovative deposition strategy can be easily extended to loading of platinum cocatalyst with other noble or non-noble metal seeds for promoted activities,demonstrating its good generality.Our work may provide an alternative way of depositing cocatalyst for better photocatalytic performances.

Photodeposition of earth‐abundant cocatalysts in photocatalytic water splitting:Methods,functions,and mechanisms

Photocatalytic water splitting based on semiconductor photocatalysts is a promising approach for producing carbon‐neutral,sustainable,and clean H_(2) fuel.Cocatalyst loading,which is an appealing strategy,has been extensively employed to improve the photocatalytic efficiency semiconductors.In view of the high cost and rare preservation of noble metal cocatalysts that significantly hinder their utilization for large‐scale energy production,various cocatalysts comprising earth‐abundant ele‐ments have been developed as noble‐metal‐free candidates using different methods to boost pho‐tocatalytic water splitting.Among these preparation strategies,photodeposition has attracted tre‐mendous attention in the deposition of earth‐abundant cocatalysts owing to its simplicity and mod‐erate availability,improved interfacial charge separation and transfer,and abundant active sites on the surface.In this review,we first summarize the deposition principles,deposition advantages,categories of cocatalysts,roles of cocatalysts,influencing factors,modification strategies,and design considerations in the photodeposition of earth‐abundant cocatalysts.The photodeposited earth‐abundant cocatalysts for the photocatalytic H_(2) evolution half reaction,photocatalytic O_(2) evo‐lution half reaction,and overall photocatalytic water splitting are discussed.Finally,some perspec‐tives on the challenges and possible future directions for the photodeposition of earth‐abundant cocatalysts in photocatalytic water splitting are presented.

Preparation, Characterization and Photocatalytic Property of Ag-loaded TiO_2 Powders Using Photodeposition Method

The Ag particles were photodeposited on TiO2 powder surface. The X-ray diffraction （XRD）, Raman spectroscopy, transmittance electron microscopy （TEM）, UV-vis diffused reflection spectroscopy （DRS）, X-ray photoelectron spectroscopy （XPS）, and photoluminescence （PL） spectrophotoscopy were used to investigate the structure and morphologies of the samples. It is found that the loaded Ag particles have no effect on the XRD patterns, and the Raman scattering becomes much stronger due to the surface Raman enhancing effect. The TEM images show that the TiO2 grains are in the shape of short sticks, and the spherical Ag particles with hexagonal structure are adhered to the TiO2 grain surface tightly. XPS result shows that the loaded Ag particles can not affect the chemical states of Ti and O, and they are mainly in the form of metal Ag. A wide plasmon absorption appears on the UV-vis spectra after Ag photodeposition. The loaded Ag further greatly decreases the PL intensity, which partly indicates the electron transfer from TiO2 to Ag. The photocatalytic activities firstly increase with the content of loaded Ag, and then sharply decrease. Finally, the photocatalytic mechanism related to Ag-loaded TiO2 powders was discussed in detail.

M@MIL-100（Fe） （M = Au, Pd, Pt） nanocomposites fabricated by a facile photodeposition process： Efficient visible-light photocatalysts for redox reactions in water

Proper design and preparation of high-performance and stable dual functional photocatalytic materials remains a significant objective of research. In this work, highly dispersed noble-metal nanoparticles （Au, Pd, Pt） were immobilized on MIL-100（Fe） （denoted M@MIL-100（Fe）） using a facile room-temperature photodeposition technique. The resulting M@MIL-100（Fe） （M = Au, Pd, and Pt） nanocomposites exhibited enhanced photoactivities toward photocatalytic degradation of methyl orange （MO） and reduction of heavy-metal Cr（VI） ions under visible-light irradiation （A ≥ 420 nm） compared with blank-MIL-100（Fe）. Combining these results with photoelectrochemical analyses revealed that noble-metal deposition can effectively improve the charge-separation efficiency of MIL-100（Fe） under visible-light irradiation. This phenomenon in turn leads to the enhancement of visible-light-driven photoactivity of M@MIL-100（Fe） toward photocatalytic redox reactions. In particular, the Pt@MIL-100（Fe） with an average Pt particle size of 2 nm exhibited remarkably enhanced photoactivities compared with those of M@MIL-100（Fe） （M = Au and Pd）, which can be attributed to the integrative effect of the enhanced light absorption intensity and more efficient separation of the photogenerated charge carrier. In addition, possible photocatalytic reaction mechanisms are also proposed.

Photodeposition fabrication of hierarchical layered Co-doped Ni oxyhydroxide(NixCo1−xOOH)catalysts with enhanced electrocatalytic performance for oxygen evolution reaction

Highly active,durable and inexpensive oxygen evolution reaction(OER)catalysts are crucial for achieving practical and high-efficiency water splitting.Herein,hierarchical interconnected NixCo1−xOOH nanosheet arrays supported on TiO2/Ti substrate have been fabricated through a facile photodeposition method.Compared with pristine NiOOH,the obtained NixCo1−xOOH nanosheet arrays possess larger exposed electrochemical active surface area,faster transfer and collection of electrons and stronger electronic interaction,showing a low overpotential of 350 mV at a current density of 10 mA·cm−2 and a small Tafel slope of 41 mV·dec−1 in basic solutions,with the OER performance superior to pristine NiOOH and most Ni-based catalysts.Furthermore,the NixCo1−xOOH electrode demonstrates excellent stability at the current density of 10 mA·cm−2 for 24 hours,which is attributed to the structural maintenance caused by the good adhesion of the catalyst and the substrate.Our study provides an alternative approach for the rational design of highly active and promising OER electrocatalysts.

Triethanolamine-mediated photodeposition formation of amorphous Ni-P alloy for improved H2-evolution activity of g-C3N4

Developing efficient,stable,and low-cost novel electron-cocatalysts is crucial for photocatalytic hydrogen evolution reaction.Herein,amorphous Ni-P alloy particles were successfully modified onto g-C3N4 to construct the Ni-P/g-C3N4 photocatalyst through a simple and green triethanolamine(TEOA)-mediated photodeposition method.It was found that the TEOA could serve as an excellent complexing agent to coordinate with Ni2+to form[Ni(TEOA)]^2+complex,which can promote the rapid and effective deposition of amorphous Ni-P alloy on the g-C3N4 surface.Photocatalytic tests suggest that the hydrogen-evolution performance of gC3N4 can be greatly promoted through integrating amorphous Ni-P alloy.Especially,the Ni-P/g-C3N4(5 wt%)exhibits the superior H2-generation activity(118.2μmol h^-1g^-1),which is almost 35.8 times that of bare g-C3N4.Furthermore,the amorphous Ni-P alloy cocatalyst can also serve as the general hydrogen-production cocatalyst to greatly enhance the photocatalytic performance of traditional semiconductor materials such as Ti O2 and Cd S.Based on the present results,the mechanism of the amorphous Ni-P alloy as the high-efficiency electron transfer medium was proposed for the boosted H2-generation rate.The present facile route may broaden the horizons for the efficient development of highly active cocatalysts in photocatalytic field.

Photodeposition of CoOx and MoS2 on CdS as dual cocatalysts for photocatalytic H2 production

Photocatalytic Hproduction from water splitting has a promising prospect for alleviating energy and environmental issues.However,the fast recombination of photogenerated charge carriers limits the photocatalytic efficiency and its practical application.Cocatalyst engineering is an effective strategy to spatially separate photogenerated charge carriers.In this work,noble-metal-free MoSand CoOcocatalysts are loaded on CdS nanorods by a two-step photodeposition method.The MoSfunctions as the reduction cocatalyst to trap electrons and Co Oas the oxidation cocatalyst to trap holes.Transmission electron microscopy(TEM),inductively coupled plasma(ICP),X-ray photoelectron spectroscopy(XPS)and MottSchottky results demonstrate the effectiveness of photodeposition for loading MoSand CoOdual cocatalysts on CdS and their impact on the photochemical properties.The optimized CdS-MoS-CoOcomposite exhibits a high photocatalytic H-production rate of 7.4 mmol g^(-1)h^(-1)and an apparent quantum efficiency(QE)of 7.6%at 420 nm.Further analysis on time-resolved photoluminescence(TRPL)indicates that the introduction of dual cocatalysts greatly prolongs the lifetime of photogenerated charge carriers and deceases the charge recombination rates,consequently leading to superior photocatalytic H-production performance.This work provides a facile and effective strategy for the construction of highly efficient dual-cocatalyst-modified CdS photocatalyst for high-performance photocatalytic Hproduction.

Simultaneous realization of direct photodeposition and high H_(2)-production activity of amorphous cobalt sulfide nanodot-modified rGO/TiO_(2)photocatalyst

To realize highly efficient hydrogen production of graphene-based photocatalysts,it is greatly important to increase more interfacial active sites onto graphene.In this work,the highly efficient CoS_(x)-rGO(reduced graphene oxide)/TiO_(2) composite photocatalyst was synthesized via a simple two-step method,including the hydrothermal loading of rGO nanosheets onto TiO_(2) nanoparticles and the subsequent photodeposition process of CoS_(x) nanodots(0.5-2 nm) on the rGO nanosheets.Photocatalytic experimental results confirmed that the CoS_(x)-rGO/TiO_(2) photocatalyst displayed a distinctly higher photocatalytic H_(2)-evolution activity than the TiO_(2) photocatalyst.The highest hydrogen-production efficiency of obtained CoS_(x)-rGO/TiO_(2)(10%) achieved 256.97 μmol·h-1,which was distinctly higher than that of TiO_(2)(4.41 μmol·h-1),rGO/TiO_(2)(20.19 μmol·h^(-1)) and CoS_(x)/TiO_(2)(132.67 μmol·h^(-1)).According to the results of various characterizations and tests,the synergistic-effect mechanism of CoS_(x) nanodots and rGO nanosheets is proposed to explain the increased photocatalytic performance of Co S_(x)-rGO/TiO_(2) photocatalytic material,namely the rGO nanosheets cause the quick transfer of photo-induced carriers from TiO_(2) to CoS_(x) nanodots,and then CoS_(x) nanodots work as hydrogenproduction active sites to quickly generate H_(2).The present study may offer innovative ideas for the preparation and application of new highly efficient and inexpensive photocatalytic materials.

Room-temperature photodeposition of conformal transition metal based cocatalysts on BiVO4 for enhanced photoelectrochemical water splitting

Photoelectrochemical(PEC)water splitting using semiconductors offers a promising way to convert renewable solar energy to clean hydrogen fuels.However,due to the sluggish reaction kinetics of water oxidation,significant charge recombination occurred at the photoanode/electrolyte interface and cause decrease of its PEC performance.To reduce the surface recombination,we deposit different transition metal complexes on BiVO4 nanocone arrays by a versatile light driven in-situ two electrode photodeposition approach without applied bias.Conformal cobalt phosphate“Co-Pi”,nickel borate“Ni-Bi”and manganese phosphate“Mn-Pi”complexes were deposited on BiVO4 nanocone arrays to form core-shell structure photoanode,all of which lead to enhanced photoelectrochemical performance.The photocurrent of the Co-Pi/BiVO4 photoanode under front-side illumination for 5 min is increased by 4 folds comparing to that of bare BiVO4 photoanode at 0.6 V vs.RHE,reaching a hole transfer efficiency as high as 94.5%at 1.23 V vs.RHE.The proposed photodeposition strategy is simple and efficient,and can be extended to deposite cocatalyst on other semiconductors with a valence band edge located at a potential more positive than the oxidation potential of transition metal ion in the cocatalyst.

Morphology of metal nanoparticles photodeposited on TiO_2/silical gel and photothermal activity for destruction of ethylene

The morphology of supported metal nanoparticles on TiO2/silical gel （TSO） and photothermal synergism were investigated for destruction of ethylene. During photocatalytic deposition of metal nanopartilces, the effects of pH and light intensity on the morphology of coated platinum, palladium, gold on TiO2/silical gel were studied. Moreover, these catalysts were characterized by TEM, UV-Vis DRS. The pH of preparing solution have strong influence on dispersion, size and sites of Pt, Pd and Au on TSO, which were controlled by the electrostatic binding of HPtCl5^- AuCl4^- and TiOH2^＋, Pd^2＋ and TiO^- respectively. Platinum, gold and palladium nanoparticles were uniformly highly dispersed on the titanol sites not silanol of TiO2/silical gel under pH=2, pH =9.9 respectively. For the photodegradation of ethylene, they show higher photothermal efficiency than those prepared with other pH conditions under UV illumination in a non-circulating photoreactor. The optimum weight loadings of Pt, Au, and Pd were 0.25 wt%, 0.5 wt%, 1 wt%, respectively. The synergistic effect enhanced ethylene removal and CO2 production. Thcse results verify that the best photothermal synergistic effect depends on the dispersion, size of noble metal nano-particles. FTIR analyses of the used Pt-, Pd-TSO catalysts indicated that no significant by-products were accumulated on the surface of the catalysts, leading to them longer lifetime.

Photochemical synthesis and enhanced photocatalytic activity of MnO_x/BiPO_4 heterojunction

Monoclinic BiPO4with rod-like shape was prepared via a CTAB-assisted hydrothermal route.MnOx nanoparticles were loaded on the surfaces of BiPO4rods by a photo-deposition process to form MnOx/BiPO4heterojunctions.The as-prepared samples were characterized by XRD,SEM,TEM,XPS,FL,and UV-Vis diffuse reflectance measurements.The results showed that MnOx nanoparticles were strongly anchored to the surfaces of BiPO4rods when the mole ratio of Mn to Bi was controlled at a low level,forming MnOx/BiPO4heterojunctions with effective and sound interfaces.The MnOx/BiPO4heterojunctions exhibited higher photoactivity than pristine BiPO4for photodegradation of methyl blue under UV irradiation,which could be attributed to the efficient charge transfer at the heterojunction interfaces.The higher light absorption ability of MnOx/BiPO4in the range of300?420nm compared with pristine BiPO4was also responsible for the enhanced photocatalytic activities of MnOx/BiPO4heterojunctions.

Evaluation of the plasmonic effect of Au and Ag on Ti-based photocatalysts in the reduction of CO2 to CH4

Crystalline TiO（P25） and isolated titanate species in a ZSM-5 structure（TS-1） were modified with Au and Ag, respectively, and tested in the gas-phase photocatalytic COreduction under high purity conditions. The noble metal modification was performed by photodeposition. Light absorbance properties of the catalysts are examined with UV–Vis spectroscopy before and after the activity test. In the gas-phase photocatalytic COreduction, it was observed that the catalysts with Ag nanostructures are more active than those with Au nanostructures. It is thus found that the energetic difference between the band gap energy of the semiconductor and the position of the plasmon is influencing the photocatalytic activity.Potentially, plasmon excitation due to visible light absorption results in plasmon resonance energy, which affects the excitation of the semiconductor positively. Therefore, an overlap between band gap energy of the semiconductor and metal plasmon is needed.

Controllable photochemical synthesis of amorphous Ni(OH)2 as hydrogen production cocatalyst using inorganic phosphorous acid as sacrificial agent

Loading of cocatalysts can effectively inhibit the recombination of photogenerated carriers in photocatalysts and greatly improve the photocatalytic hydrogen production rate. Cocatalysts can be deposited at the outlet points of electrons using a photochemical method, which is beneficial for the following photocatalytic hydrogen production reaction. H2PO2^– has been used in the photochemical reduction of transition metals because of its special properties. However, the particles formed in the presence of H2PO2^– are very large and highly crystalline, which may inhibit the activity of photocatalysts. In this study, we designed a new method for synthesizing photocatalysts by photodeposition using some other phosphates, aiming to prepare controllable weakly crystalline and small-size cocatalysts to improve the hydrogen production activity. The cocatalyst prepared using H2PO3^– as an inorganic sacrificial agent has an amorphous structure and an average size of about 10 nm. The optimal photocatalytic hydrogen production rate of the obtained Ni(OH)2/g-C3N4(4.36 wt%) is 13707.86 μmol·g^-1·h^-1, which is even higher than the activity of Pt-4.36 wt%/g-C3N4(11210.93 μmol·g^-1·h^-1). Mechanistic studies show that loading of Ni(OH)2 can efficiently accelerate the separation and transfer efficiency of photogenerated charge carriers.

Fluorescence Properties of the Lanthanide Supported onto Titanate Nanosheets

Metal oxide nanosheets are increasingly used as catalysts, hard coatings and transparent thin films. Among these materials, TNSs （Titanate Nanosheets） synthesized in liquid phase enjoy particular attention due to their water dispersibility, photocatalytic activity, unique morphology and ease of synthesis. Importantly, the photo-induced redox reaction between TNSs and metal oxides affords potentially fluorescent metal-supported TNSs with enhanced photocatalytic activity, e.g., Ln/TNSs （Lanthaide-supported TNSs）. Herein, TNSs doped with arbitrary amounts of group 5 elements （M-TNSs： M = V, Nb and Ta） were prepared to investigate the fluorescent excitation spectra of Ln/M-TNSs and thus shed light on the mechanism of photodeposition and determine the origin of Ln/TNS fluorescence. As a result, photodepositiom was shown to involve phot-induced redox reaction between TNSs and lanthanide oxides, and the fluorescence intensity of Ln/TNSs and Ln/M-TNSs was demonstrated to be determined by the overlap of TNS and Ln3＋ excitation energies.

Three-dimensional CeO_(2)@carbon-quantum-dots scaffold modified with Au nanoparticles on flexible substrates for high performance gas sensing at room temperature

High-performance gas sensing materials operated at room temperature(RT) are attractive for a variety of real-time gas monitoring applications,especially with the excellent durability and flexibility of wearable sensor.The constructing heterostructure is one of the significant approaches in design strategies of sensing materials.This heterostructure effectively increases the active site for improving sensing performance and decreasing energy consumption.Herein,the heterostructure of Au nanoparticles modified CeO_(2)@carbon-quantum-dots(Au/CeO_(2)@CQDs) with a three-dimensional(3D) scaffold structure are successfully synthesized by an effective strategy,which can apply for preparing flexible gas sensor.The gas sensing properties of Au/CeO_(2)@CQDs based on flexible substrate are obtained under long-term repeated NO_(2) exposure at RT.Meanwhile,the long-term mechanical stability of this gas sensing device is also detected after different bending cycles.The Au/CeO_(2)@CQDs based on flexible substrate sensor exhibits excellent performance,including higher sensitivity(47.2),faster response(18 s)and recovery time(22 s) as well as longer-term stability than performance of pure materials.The obtained sensor also reveals outstanding mechanical flexibility,which is only a tiny response fluctuation(8.1%) after 500 bending/relaxing cycles.Therefore,our study demonstrates the enormous potential of this sensing materials for hazardous gas monitoring in future portable and wearable sensing platform.

Effect of platinum on the photocatalytic degradation of chlorinated organic compound

TiO 2 nanoparticles, doped with different Pt contents, were prepared by a modified photodeposition method using Degussa P-25 TiO 2 , H 2 PtCl 6 ·6H 2 O and methanol as the solvents. The physicochemical properties of Pt/TiO 2 were investigated by the nitrogen adsorption and desorption isotherm measurement technique, X-ray diffraction analysis and photoluminescence spectra, respectively. Reaction rates from photocatalytic removal of dichloromethane over Degussa P-25 TiO 2 and Pt/TiO 2 were evaluated. The average diameter and BET surface area of the TiO 2 catalyst particles were 300 nm and 50 m 2 /g, respectively. The degradation efficiency was 99.0%, 82.7%, 55.2%, and 57.9% with TiO 2 at inlet concentrations of 50, 100, 200, and 300 ppm, respectively. And the degradation efficiency was 99.3%, 79.7%, 76.5%, and 73.4% with a 0.005 wt.% Pt/TiO 2 at inlet concentrations of 50, 100, 200, and 300 ppm, respectively. In addition, we found that the photoluminescence emission peak intensities decreased with increases in the doping amount of Pt, which indicates that the irradiative recombination was weakened. Furthermore, the results showed that the UV/0.005 wt.% Pt/TiO 2 process was capable of efficiently decomposing gaseous DCM in air.

Photodeposited metal-semiconductor nanocomposites and their applications

While two-dimensional layered nanomaterials including transition metal oxides and transition metal dichalcogenides have been widely researched because of their unique electronic and optical properties,they still have some limitations.To overcome these limitations,transition metal oxides and transition metal dichalcogenides based nanocomposites have been developed using various methods and have exhibited superior properties.In this paper,we introduce the photodeposition method and review the photodeposition of metal nanoparticles on the surface of transition metal oxide and transition metal dichalcogenides.Their current applications are also explained,such as photocatalysis,hydrogen evolution reaction,surface enhanced Ramanscattering,etc.This approach for nanocomposites has potential for future research areas such as photocatalysis,hydrogen evolution reaction,surface enhanced Raman scattering,and other applications.This approach for nanocomposite has the potential for future research areas.

Rationally designed/constructed MnO_x/WO_3 anode for photoelectrochemical water oxidation

Photoelectrocatalytic water splitting is an effective way to utilize the solar energy to solve the energy shortage. The valence band edge of WO3 located at 3V vs. normal hydrogen electrode（NHE）, which can offer enough potential to kinetically oxidize water for oxygen evolution reaction. However, water oxidation reaction kinetics is sluggish when only WO3 is used as the photoanode. It is highly desirable to use cocatalyst to promote the kinetics. Mn Oxloaded on the WO3 photoanode through photodeposition methods improves the photoelectrochemical water oxidation performance. A maximum photocurrent density of composite photoanode is achieved with a deposition time of 3 min, which is higher than that of pristine WO3 photoanode around 40%. Mn O2 is not only a cocatalyst for water splitting but also for improving oxidation selectivity. We tried to use two means to load Mn Oxon WO3 photoanode material. It is observed that loading a moderate amount of Mn Oxon the WO3 by photodeposition can promote the performance of the WO3 photoanode.