Solar-driven CO_(2) conversion to methane and methanol using different nanostructured Cu_(2)O-based catalysts modified with Au nanoparticles

This work describes the use of TiO_(2)nanotubes-based electrodes(TNT)modified with Cu_(2)O nanostructures and gold nanoparticles for the photoelectroreduction of CO_(2)to produce value-added compounds.A thin layer of polydopamine was used as both an adherent agent and an electron transfer mediator,due to itsπ-conjugated electron system.The highest production yield was achieved using a TNT@PDA/Nc/Au40%electrode,with Faradaic efficiencies of 47.4%(110.5μM cm^(-2))and 27.8%(50.4μM cm^(-2))for methanol and methane,respectively.The performance of the photoelectrodes was shown to be Cu_(2)O facet-dependent,with cubic structures leading to greater conversion of CO_(2)to methanol(43%)and methane(27%),compared to the octahedral morphology,while a higher percentage of metallic gold on the nanostructured Cu_(2)O surface was mainly important for CH4production.Density functional theory(DFT)calculations supported these findings,attributing the superior photoelectrocatalytic performance of the TNT@PDA/Nc/Au40%electrode for CH4generation to the formation of an OCH3intermediate bonded to Au atoms.Studies using isotope-labeling and analysis by gas chromatograph-mass(GC-MS)demonstrated that13CO_(2)was the source for photoelectrocatalytic generation of13CH3OH and13CH313CH2OH.

Flexible hollow TiO_(2)@CMS/carbon-fiber van der Waals heterostructures for simulated-solar light photocatalysis and photoelectrocatalysis

The recycling technology of photocatalyst powdery has hardly been mature in the photocatalytic oxidation so far.In this work,the hollow TiO_(2)microspheres with an appropriate thickness are confined in carbon microspheres(CMSs)to form hollow TiO_(2)@CMSs,which are physically integrated with carbon-fiber textile by van der Waals(vdW)interactions to generate separable and recyclable hollow TiO_(2)@CMSs/carbon-fiber vdW heterostructures.Such separable and recyclable heterostructures show remarkable oxidation of 2,4-dinitrophenol.From our detailed characterization and density functional theory(DFT)calculations,we found that carbon fiber can trap electrons exerted from the excitation of hollow TiO_(2)@CMSs and creates holes in hollow TiO_(2)microspheres,which endow the carbon fiber with photocatalytic activity through coherent charge injection.This study indicates that our general strategy for the fabrication of hollow TiO_(2)@CMSs/carbon-fiber vdW heterostructures can be used as separable and recyclable photocatalyst and photoelectrocatalyst with potential industrial applications in environmentrelated fields.

Photoelectrocatalytic principles for meaningfully studying photocatalyst properties and photocatalysis processes:From fundamental theory to environmental applications

Photocatalysis is critically important for environmental remediation and renewable energy technologies.The ability to objectively characterize photocatalyst properties and photocatalysis processes is paramount for meaningful performance evaluation and fundamental studies to guide the design and development of high-performance photocatalysts and photocatalysis systems.Photocatalysis is essentially an electron transfer process,and photoelectrocatalysis(PEC)principles can be used to directly quantify transferred electrons to determine the intrinsic properties of photocatalysts and photocatalysis processes in isolation,without interference from counter reactions due to physically separated oxidation and reduction half-reactions.In this review,we discuss emphatically the PEC-based principles for characterizing intrinsic properties of photocatalysts and important processes of photocatalysis,with a particular focus on their environmental applications in the degradation of pollutants,disinfection,and detection of chemical oxygen demand(COD).An outlook towards the potential applications of PEC technique is given.

A review on photo-, electro- and photoelectro- catalytic strategies for selective oxidation of alcohols

Traditional conversion of alcohols into carbonyl compounds exists a few drawbacks such as harsh reaction conditions,production of large amounts of hazardous wastes,and poor selectivity.The newly emerging conversion approaches via photo-,electro-,and photoelectro-catalysis to oxidize alcohols into high value-added corresponding carbonyl compounds as well as the possible simultaneous production of clean fuel hydrogen(H_(2))under mild conditions are promising to substitute the traditional approach to form greener and sustainable reaction systems and thus have aroused tremendous investigations.In this review,the state-of-the-art photocatalytic,electrocatalytic,and photoelectrocatalytic strategies for selective oxidation of different types of alcohols(aromatic and aliphatic alcohols,single alcohol,and polyols,etc.)as well as the simultaneous production of H_(2) in certain systems are discussed.The design of photocatalysts,electrocatalysts,and photoelectrocatalysts as well as reaction mechanism is summarized and discussed in detail.In the end,current challenges and future research directions are proposed.It is expected that this review will not only deepen the understanding of environmentally friendly catalytic systems for alcohol conversion as well as H_(2) production,but also enlighten significance and inspirations for the follow-up study of selective oxidation of various types of organic molecules to value-added chemicals.

Molecular insight into the GaP(110)-water interface using machine learning accelerated molecular dynamics

GaP has been shown to be a promising photoelectrocatalyst for selective CO_(2)reduction to methanol.Due to the relevance of the interface structure to important processes such as electron/proton transfer,a detailed understanding of the GaP(110)-water interfacial structure is of great importance.Ab initio molecular dynamics(AIMD)can be used for obtaining the microscopic information of the interfacial structure.However,the GaP(110)-water interface cannot converge to an equilibrated structure at the time scale of the AIMD simulation.In this work,we perform the machine learning accelerated molecular dynamics(MLMD)to overcome the difficulty of insufficient sampling by AIMD.With the help of MLMD,we unravel the microscopic information of the structure of the GaP(110)-water interface,and obtain a deeper understanding of the mechanisms of proton transfer at the GaP(110)-water interface,which will pave the way for gaining valuable insights into photoelectrocatalytic mechanisms and improving the performance of photoelectrochemical cells.

The Inhibition Effect of Tert-Butyl Alcohol on the TiO_2 Nano Assays Photoelectrocatalytic Degradation of Different Organics and Its Mechanism

The inhibition effect of tert-butyl alcohol(TBA), identified as the·OH radical inhibitor, on the TiO_2 nano assays(TNA) photoelectrocatalytic oxidation of different organics such as glucose and phthalate was reported. The adsorption performance of these organics on the TNA photoelectrode was investigated by using the instantaneous photocurrent value, and the degradation property was examined by using the exhausted reaction. The results showed that glucose exhibited the poor adsorption and easy degradation performance, phthalate showed the strong adsorption and harddegradation, but TBA showed the weak adsorption and was the most difficult to be degraded. The degradation of both glucose and phthalate could be inhibited evidently by TBA. But the effect on glucose was more obvious. The different inhibition effects of TBA on different organics could be attributed to the differences in the adsorption and the degradation property. For instance, phthalate of the strong adsorption property could avoid from the capture of·OH radicals by TBA in TNA photoelectrocatalytic process.

Nickel and indium core-shell co-catalysts loaded silicon nanowire arrays for efficient photoelectrocatalytic reduction of CO_(2) to formate

Developing an efficient artificial photosynthetic system for transforming carbon dioxide and storing solar energy in the form of chemical bonds is one of the greatest challenges in modern chemistry.However,the limited choice of catalysts with wide light absorption range,long-term stability and excellent selectivity for CO_(2) reduction makes the process sluggish.Here,a core-shell-structured nonnoble-metal Ni@In co-catalyst loaded p-type silicon nanowire arrays(SiNWs)for efficient CO_(2) reduction to formate is demonstrated.The formation rate and Faradaic efficiency of formate over the Ni@In/SiNWs catalyst reach 58μmol h^(-1) cm^(-2) and 87% under the irradiation of one simulated sunlight(AM 1.5 G,100 mW cm^(-2)),respectively,which are about 24 and 12 times those over the pristine SiNWs.The enhanced photoelectrocatalytic performance for CO_(2) reduction is attributed to the rational combination of Ni capable of effectively extracting the photogenerated electrons and In responsible for the selective activation of CO_(2).

Highly Efficient Photoelectrocatalytic Reduction of CO2 to Methanol by a p–n Heterojunction CeO2/CuO/Cu Catalyst

Photoelectrocatalytic reduction of CO2 to fuels has great potential for reducing anthropogenic CO2 emissions and also lessening our dependence on fossil fuel energy.Herein,we report the successful development of a novel photoelectrocatalytic catalyst for the selective reduction of CO2 to methanol,comprising a copper catalyst modified with flower-like cerium oxide nanoparticles(CeO2 NPs)(a n-type semiconductor)and copper oxide nanoparticles(CuO NPs)(a p-type semiconductor).At an applied potential of−1.0 V(vs SCE)under visible light irradiation,the CeO2 NPs/CuO NPs/Cu catalyst yielded methanol at a rate of 3.44μmol cm^−2 h^−1,which was approximately five times higher than that of a CuO NPs/Cu catalyst(0.67μmol cm^−2 h^−1).The carrier concentration increased by^108 times when the flower-like CeO2 NPs were deposited on the CuO NPs/Cu catalyst,due to synergistic transfer of photoexcited electrons from the conduction band of CuO to that of CeO2,which enhanced both photocatalytic and photoelectrocatalytic CO2 reduction on the CeO2 NPs.The facile migration of photoexcited electrons and holes across the p–n heterojunction that formed between the CeO2 and CuO components was thus critical to excellent light-induced CO2 reduction properties of the CeO2 NPs/CuO NPs/Cu catalyst.Results encourage the wider application of composite semiconductor electrodes in carbon dioxide reduction.

Photoelectrocatalytic oxidation of methane into methanol and formic acid over ZnO/graphene/polyaniline catalyst

ZnO/graphene/polyaniline(PANI) composite is synthesized and used for photoelectrocatalytic oxidation of methane under simulated sun light illumination with ambient conditions. The photoelectrochemical(PEC) performance of pure ZnO, ZnO/graphene, ZnO/PANI, and ZnO/graphene/PANI photoanodes is investigated by cyclic voltammetry(CV),chronoamerometry(J–t) and electrochemical impedance spectroscopy(EIS). The yields of methane oxidation products,mainly methanol(CH_3OH) and formic acid(HCOOH), catalysed by the synthesized ZnO/graphene/PANI composite are 2.76 and 3.20 times those of pure ZnO, respectively. The mechanism of the photoelectrocatalytic process converting methane into methanol and formic acid is proposed on the basis of the experimental results. The enhanced photoelectrocatalytic activity of the ZnO/graphene/PANI composite can be attributed to the fact that graphene can efficiently transfer photo-generated electrons from the inner region to the surface reaction to form free radicals due to its superior electrical conductivity as an inter-media layer. Meanwhile, the introduction of PANI promotes solar energy harvesting by extending the visible light absorption and enhances charge separation efficiency due to its conducting polymer characteristics.In addition, the PANI can create a favorable π-conjunction structure together with graphene layers, which can achieve a more effective charge separation. This research demonstrates that the fabricated ZnO/graphene/PANI composite promises to implement the visible-light photoelectrocatalytic methane oxidation.

Determination of hydroxyl radicals in TiO2/Ti photoelectrocatalytic oxidation system using Fe（phen）3^2＋ spectrophotometry

A new method of determining the cumulate concentration of hydroxyl radicals in the TiO2/Ti photoelectrocatalytic（PEC） oxidation system was established by o-phenanthroline-Fe（Ⅱ）（Fe（phen）3^2＋） spectrophotometry and using anion exchange membrane. Fe （phen）3^2＋ can be oxidized to o-phenanthroline-Fe（Ⅲ）（Fe（phen）3^3＋） by strong oxidization of hydroxyl radicals（·OH）. Then the cumulate concentration of hydroxyl radicals can be calculated through determining the change of the Fe（phen）3^3＋ absorbency at 509 nm. In addition, the research results showed the production rate of hydroxyl radicals was affected obviously by pH of solution, the cumulate concentration of hydroxyl radicals was the largest at nearby the initial pH 6.3 （isoelectric point）, and the change direction of pH after illumination tended to nearby isoelectric point.

Perovskite–A wonder catalyst for solar hydrogen production

Hydrogen generation via artificial photosynthesis paves a promising way to remit the ever-increasing energy crisis and deteriorative environmental issues.Among all the materials utilized for solar hydrogen production,perovskite has emerged as a rising star due to its superior optoelectronic properties.This manuscript aims to provide a comprehensive review summarizing the recent inspiring advancements on perovskite-based solar hydrogen production systems,including the particulate photocatalysis,photoelectrochemical cells,and photovoltaic-electrocatalytic cells.We start with a brief introduction of the advantages of perovskites for solar hydrogen production and the basic principles of the three most prominent solar hydrogen production systems.The representative progresses in this field are then detailed with a special emphasis on the strategies to improve the efficiency and the stability of the systems.Finally,challenges and opportunities for the further development of the PVK-based solar hydrogen production systems are presented with perspective given on outlook,performance,cost and stability.

Plasmonic Ag‑Decorated Few‑Layer MoS2 Nanosheets Vertically Grown on Graphene for Efficient Photoelectrochemical Water Splitting

A controllable approach that combines surface plasmon resonance and twodimensional(2D)graphene/MoS2 heterojunction has not been implemented despite its potential for efficient photoelectrochemical(PEC)water splitting.In this study,plasmonic Ag-decorated 2D MoS2 nanosheets were vertically grown on graphene substrates in a practical large-scale manner through metalorganic chemical vapor deposition of MoS2 and thermal evaporation of Ag.The plasmonic Ag-decorated MoS2 nanosheets on graphene yielded up to 10 times higher photo-to-dark current ratio than MoS2 nanosheets on indium tin oxide.The significantly enhanced PEC activity could be attributed to the synergetic effects of SPR and favorable graphene/2D MoS2 heterojunction.Plasmonic Ag nanoparticles not only increased visible-light and near-infrared absorption of 2D MoS2,but also induced highly amplified local electric field intensity in 2D MoS2.In addition,the vertically aligned 2D MoS2 on graphene acted as a desirable heterostructure for efficient separation and transportation of photo-generated carriers.This study provides a promising path for exploiting the full potential of 2D MoS2 for practical large-scale and efficient PEC water-splitting applications.

Photoelectrochemical regeneration of all vanadium redox species for construction of a solar rechargeable flow cell

Energy storage is pivotal for the continuous utilization of solar energy suffering from the intermittency issue. Herein, we demonstrate a solar rechargeable flow cell（SRFC） based on photoelectrochemical regeneration of vanadium redox species for in-situ solar energy harvest and storage. In this device, TiO_2 and MWCNT/acetylene black（MWCNT/AB） composite are served as the photoanode and the counter electrode,respectively, with all vanadium redox couples, VO_2~＋/VO^（2＋）and VO^（2＋）/V^（3＋）, as solar energy storage media.Benefitting from solar energy, the cell can be photocharged under a bias as low as 0.1 V, which is much lower than the discharge voltage of ~0.5 V. Photocharged under the optimized condition, the cell delivers a discharge energy of 23.0 mWh/L with 67.4% input electric energy savings. This prototype work may inspire the rational design for cost-effective solar energy storage devices.

Visible Light Photoelectrocatalytic Degradation of Rhodamine B Using Ti/TiO2-NiO Photoanode

The method of Ti/TiO2-NiO photoelectrode prepared by using sol-gel method continued by calcination process was introduced. The prepared TiO2-NiO film was observed with XRD and TEM. The anatase-rutile TiO2 was mainly on the prepared TiO2-NiO composite surface electrode. In addition to NiO, the composite also formed NiTiO3 that increased with increasing calcination temperature. Photoelectrocatalytic degradation of Rhodamine B (RB) using this electrode was investigated, and anodic potential and pH were optimized. RB degradation was investigated under different conditions, and it showed that photoelectrocatalytic degradation could achieve efficient and complete mineralization of organic pollutant. Through comparison of the photoelectrocatalytic oxidation using the Ti/TiO2-NiO electrode operated by single photoanode with the Ti/TiO2-NiO electrode operated by several photoanode, it was found that the photoelectrocatalytic efficiency of that by series photoanodes was higher. Additionally, photoelectrocatalytic system was performed at the several different photoelectrodes, which verified the higher photocatalytic activity compared with the single photoelectrode.

Photoelectrocatalytic hydrogen evolution and synchronous degradation of organic pollutants by pg-C_(3)N_(4)/β-FeOOH S-scheme heterojunction

Crafting photoelectrocatalytic materials with robust oxidation-reduction properties for simultaneous hydrogen evolution and pollutant degradation poses a formidable challenge.In this study,a pg-C_(3)N_(4)/β-FeOOH S-scheme heterostructure with a special energy band structure was developed by anchoring porous pg-C_(3)N_(4)on needle shapedβ-FeOOH.Functioning as a hole extraction layer,needle-leaf-likeβ-FeOOH can facilitate efficient hole migration and enhance charge transport.Remarkably,the optimized 0.2-pg-C_(3)N_(4)/β-FeOOH could degrade 78%of ofloxacin(OFLO)in 90 min.The organic pollutants could absorb a large number of holes,which prompted a greater proportion of photogenerated electrons to actively participate in the hydrogen evolution reaction at the cathode.Consequently,the hydrogen production of 0.2-pg-C_(3)N_(4)/β-FeOOH reached 1452.88μmol cm^(-2)h^(-1),exhibiting a notable increase of 61.81-165.12μmol cm^(-2)h^(-1)compared with that in the absence of pollutants.Experimental and theoretical calculation results underscore that this investigation is grounded in a distinctive electron and hole dual channel transfer mechanism.These findings offer novel insights for the future development of S-scheme heterojunction photoelectrocatalytic materials capable of concurrently degrading pollutants and promoting hydrogen evolution.

Surface amorphization oxygen vacancy-rich porous Sn_(3)O_(x)nanosheets for boosted photoelectrocatalytic bacterial inactivation

Antibiotic misuse has resulted in the emergence of superbugs,warranting new antibacterial methods.Surface amorphisation oxygen vacancy-rich porous Sn_(3)O_(x)nanosheets in situ grown on Ni foam are successfully designed via a simple,one-step hydrothermal method,resulting in enhanced photoelectrochemical(PEC)bacterial inactivation.In this system,the porous structure enriches its surface with oxygen vacancies,which can extend the absorption spectrum into the near-infrared region,while oxygen vacancies can enhance the separation of electronhole pairs.Most importantly,the sheet-like porous structure enhances surface active sites and increase the contact area between bacteria and electrodes.Therefore,the reactive oxygen species produced during the PEC process can directly act on the surface of bacteria and is100%effectively against drug-resistant Gram-positive and Gram-negative bacteria in water within 30 min.This study acts as a foundation for the development of novel photoelectrocatalyst electrodes for efficient water purification.

Defect-designed Mo-doped BiVO_(4)photoanode for efficient photoelectrochemical degradation of phenol

The monoclinic scheelite BiVO_(4)has impressive properties such as a narrow energy band gap,exceptional stability,and extended absorption in visible light,making it a suitable photoanode.Nevertheless,the BiVO_(4)material encounters challenges such as the high recombination rate of photogenerated electronhole pairs and poor photoelectron conductivity,which limits photocatalytic activity.To address this problem,we developed Mo-doped BiVO_(4)films on FTO substrates for photoelectrocatalytic degradation of phenol.When exposed to visible light,the Mo-BiVO_(4)film attained a 70%degradation of phenol in 120 min with a 1.2 V vs.Ag/AgCl bias—a 3.7 times improvement from pristine BiVO_(4).Mo-doping facilitates better migration and separation of electron-hole pairs and increases the concentration of photogenerated carriers,leading to an upward shift of the valence band potential direction,and an improvement in oxidation capacity.Furthermore,density-functional theory(DFT)calculations were used to explain how Modoping with BiVO_(4)improves the adsorption energy to phenol degradation intermediates,emphasizing its effectiveness in promoting phenol degradation.Therefore,with the inclusion of DFT calculations,this work provides a more comprehensive understanding of the mechanism underlying the enhancement of photocatalytic activity by Mo-doped BiVO_(4),which is crucial information for the further development of effective and efficient photoanodes.

Solar-driven green synthesis of epoxides

Epoxides are one of the most important intermediates used in the production of valuable chemicals. Traditional preparation methods often rely on hazardous oxidants or extensive fossil fuel-powered thermal catalytic systems, resulting in significant waste production and CO_(2) emissions. Solar-driven photo(electro)chemistry is an emerging option for achieving the environmentally-friendly synthesis of epoxides. In this review, we firstly summarize the fundamental understanding of epoxidation reactions among various systems, including molecular catalysis, heterogeneous thermal catalysis and electrocatalysis. Then, we focus on the recent advances in the synthesis of epoxides achieved by photo(electro)chemical approaches. This review is concluded by the rational design of photoelectrochemical systems towards efficient epoxide synthesis.

Studies on photo-electro-chemical catalytic degradation of acid scarlet 3R dye

A new type of photo-electro-chemical catalytic reactor was designed.Cathode and anode of the new reactor were made of high-purity graphite and titanium dioxide electrode re-spectively.A saturated calomel electrode (SCE) was used as the reference electrode.Under the condition of ultraviolet radiation and anodic bias-voltage,acid scarlet 3R was degraded by the process of photoelectrocatalysis with titanium dioxide electrode in anodic compartment,while it was degraded by electrogenerated Fenton’s reagent and hydrogen peroxide through reducing dissolved oxygen with graphite electrode in catholyte.The new reactor made the best use of photogenerated holes and photogenerated charge on the anode of the new reactor,which achieved the purpose of degrading acid scarlet 3R in the cathodic and anodic compartments simultaneously,i.e.“two electrodes and double effect”.The experimental results showed that,compared with other photoelectrocatalysis reactors (“two electrodes and single effect” reactor),the new reactor has obviously enhanced the degradation of acid scarlet 3R dye.With the con-centration of the dye being 30 mg·L?1 in water,under the operating conditions that when the inert supporting electrolyte concentration was 0.02 mol·L?1 sodium sulfate,initial solution pH = 3,and cathodic potential ?Ec = 0.66 V,the highest decolorizing efficiency of 92% was accomplished in cathodic compartment,and that of 60% in anodic compartment.

Production and contribution of hydroxyl radicals between the DSA anode and water interface

Hydroxyl radicals play the key role during electrochemical oxidation and photoelectrochemical oxidation. The production and effect of hydroxyl radicals on the interface between DSA anode and water was investigated by examining the quenching effect of iso-propanol on Orange II decolorization. We observed that with an increase in electrode potential from 4 to 12 V across electrodes at pH 7.0, the contribution percentage of hydroxyl radicals increased dramatically. More OH radicals were produced in acidic and alkaline conditions than at neutral conditions. At electrode potential of 4 V, the contribution percentage of hydroxyl radicals was obviously higher at near neutral pH conditions, while removal efficiency of Orange/I achieved was the lowest concurrently. Finally, for photocatalytic oxidation, electrochemical oxidation, and photoelectrochemical oxidation using the same DSA electrode, the effect of hydroxyl radicals proved to be dominant in photocatalytic oxidation but the contribution of hydroxyl radicals was not dominant in electrochemical oxidation, which implies the necessity of UV irradiation for electrochemical oxidation during water treatment.