Photoreductive Dissolution of Schwertmannite with Incorporated As(Ⅴ) Induced by Oxalate and the Mobilization of As(Ⅴ)

Schwertmannite(Sh), a poorly crystalline iron(hydr)oxide that usually appears in acid mine drainage, plays a significant role in the immobilization of As(V). In this study, the effects of UV irradiation and oxalate on the dissolution of Sh with structurally incorporated As(V) [Sh-As(V)] and the subsequent mobilization of As(V) were investigated at pH 3.0. In the dark, more total dissolved Fe was produced(the maximum value was 33.2 mg/L) in the suspensions of Sh-As(V) with oxalate than in those without oxalate. UV irradiation slightly enhanced the mobilization of As(V) for the system of Sh-As(V)-1 and Sh-As(V)-2 in the absence of oxalate compared with that in the dark. However, in the presence of oxalate, UV irradiation caused the concentration of mobilized As(V) to decline by 630-875% compared with that in the dark. This study enhanced our understanding of the mobilization of As(V) and demonstrated that UV irradiation could contribute to the immobilization of As(V) on Sh in aqueous environments containing oxalate.

Reconcile the contradictory wettability requirements for the reduction and oxidation half-reactions in overall CO_(2) photoreduction via alternately hydrophobic surfaces

The overall photocatalytic CO_(2) reduction reaction(OPCRR)that can directly convert CO_(2) and H_(2)O into fuels represents a promising renewable energy conversion technology.As a typical redox reaction,the OPCRR involves two half-reactions:the CO_(2) reduction half-reaction(CRHR)and the water oxidation half-reaction(WOHR).Generally,both half-reactions can be promoted by adjusting the wettability of catalysts.However,there is a contradiction in wettability requirements for the two half-reactions.Specifically,CRHR prefers a hydrophobic surface that can accumulate more CO_(2) molecules on the active sites,ensuring the appropriate ratio of gas-phase(CO_(2))to liquid-phase(H_(2)O)reactants.Conversely,the WOHR prefers a hydrophilic surface that can promote the departure of the gaseous product(O_(2))from the catalyst surface,preventing isolation between active sites and the reactant(H_(2)O).Here,we successfully reconciled the contradictory wettability requirements for the CRHR and WOHR by creating an alternately hydrophobic catalyst.This was achieved through a selectively hydrophobic modification method and a charge-transfer-control strategy.Consequently,the collaboratively promoted CRHR and WOHR led to a significantly enhanced OPCRR with a solar-to-fuel conversion efficiency of 0.186%.Notably,in ethanol production,the catalyst exhibited a 10.64-fold increase in generation rate(271.44μmol g^(-1)h~(-1))and a 4-fold increase in selectivity(55.77%)compared to the benchmark catalyst.This innovative approach holds great potential for application in universal overall reactions involving gas participation.

Manipulating photogenerated electron flow in nickel single‐atom catalysts for photocatalytic CO_(2) reduction into tunable syngas

The key to designing photocatalysts is to orient the migration of photogenerated electrons to the target active sites rather than dissipate at inert sites.Herein,we demonstrate that the doping of phosphorus(P)significantly enriches photogenerated electrons at Ni active sites and enhances the performance for CO_(2) reduction into syngas.During photocatalytic CO_(2) reduction,Ni single‐atom‐anchored P‐modulated carbon nitride showed an impressive syngas yield rate of 85μmol gcat^(−1)h^(−1) and continuously adjustable CO/H_(2) ratios ranging from 5:1 to 1:2,which exceeded those of most of the reported carbon nitride‐based single‐atom catalysts.Mechanistic studies reveal that P doping improves the conductivity of catalysts,which promotes photogenerated electron transfer to the Ni active sites rather than dissipate randomly at low‐activity nonmetallic sites,facilitating the CO_(2)‐to‐syngas photoreduction process.

Boosting CO_(2) photoreduction by synergistic optimization of multiple processes through metal vacancy engineering

The photoreduction of greenhouse gas CO_(2) using photocatalytic technologies not only benefits en-vironmental remediation but also facilitates the production of raw materials for chemicals.Howev-er,the efficiency of CO_(2) photoreduction remains generally low due to the challenging activation of CO_(2) and the limited light absorption and separation of charge.Defect engineering of catalysts rep-resents a pivotal strategy to enhance the photocatalytic activity for CO_(2),with most research on met-al oxide catalysts focusing on the creation of anionic vacancies.The exploration of metal vacancies and their effects,however,is still underexplored.In this study,we prepared an In2O3 catalyst with indium vacancies(VIn)through defect engineering for CO_(2) photoreduction.Experimental and theo-retical calculations results demonstrate that VIn not only facilitate light absorption and charge sepa-ration in the catalyst but also enhance CO_(2) adsorption and reduce the energy barrier for the for-mation of the key intermediate*COOH during CO_(2) reduction.Through metal vacancy engineering,the activity of the catalyst was 7.4 times,reaching an outstanding rate of 841.32μmol g(-1)h^(-1).This work unveils the mechanism of metal vacancies in CO_(2) photoreduction and provides theoretical guidance for the development of novel CO_(2) photoreduction catalysts.

Internal electric field modulation by copper vacancy concentration of cuprous sulfide nanosheets for enhanced selective CO_(2) photoreduction

Although the internal electric field(IEF)of photocatalysts is acknowledged as a potent driving force for photocharge separation,modulating the IEF intensity to achieve enhanced photocatalytic performances remains a challenge.Herein,cuprous sulfide nanosheets with different Cu vacancy concentration were employed to study IEF modulation and corresponding direct charge transfer.Among the samples,Cu_(1.8)S nanosheets possessed intensified IEF intensity compared with those of Cu_(2)S and Cu_(1.95)S nanosheets,suggesting that an enhanced IEF intensity could be achieved by introducing more Cu vacancies.This intensified IEF of Cu_(1.8)S nanosheets induced numerous photogenerated electrons to migrate to its surface,and the dissociative electrons were then captured by Cu vacancies,resulting in efficient charge separation spatially.In addition,the Cu vacancies on Cu_(1.8)S nanosheets accumulated electrons as active sites to lower the energy barrier of rate-determining step of CO_(2)photoreduction,leading to the selective conversion of CO_(2)to CO.Herein,the manipulation of IEF intensity through Cu vacancy concentration regulation of cuprous sulfide photocatalysts for efficient charge separation has been discussed,providing a scientific strategy to rationally improve photocata lytic performances for solar energy conversion.

PdCu alloy anchored defective titania for photocatalytic conversion of carbon dioxide into methane with 100% selectivity

The photoreduction of CO_(2)into CH_(4)with simultaneous high activity and selectivity is a promising strategy to increase energy supply and alleviate global warming.However,the absence of the active sites that is responsible for the adsorption and activation of CO_(2)and the generation of CO and H2via side reactions often lead to poor efficiency and low selectivity of the catalyst.Herein,Cu,Pd,and PdCu metal clusters cocatalyst-anchored defective TiO_(2)nanotubes(Cu/TiO_(2)-SBO,Pd/TiO_(2)-SBO,and Pd1Cu1/TiO_(2)-SBO)were designed via a simple solution impregnation reduction and applied for photocatalytic conversion of CO_(2)to CH_(4).The Pd1Cu1/TiO_(2)-SBO photocatalyst exhibits excellent catalytic performance among the other catalysts for photoreduction of CO_(2)into CH_(4).More interestingly,the product selectivity of CH_(4)reaches up to 100%with a rate of 25μmol g^(-1)h^(-1).In-situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)and density functional theory(DFT)simulations indicate that the main reasons for the high selectivity of CH_(4)are attributed to the PdCu alloy and oxygen vacancies,which jointly enhance the photoinduced carrier separation and lower energy barriers of key intermediates.Moreover,due to the tunable d-band center of the Cu site in the PdCu alloy,the generated intermediates can be well prevented from poisoning and promoted to participate in further reactions.Hopefully,the current study will provide insight into the development of new,highly selective photocatalysts for the visible light-catalytic reduction of CO_(2)into CH_(4).

Strain‑Induced Surface Interface Dual Polarization Constructs PML‑Cu/Bi_(12)O_(17)Br_(2) High‑Density Active Sites for CO_(2) Photoreduction

The insufficient active sites and slow interfacial charge trans-fer of photocatalysts restrict the efficiency of CO_(2) photoreduction.The synchronized modulation of the above key issues is demanding and chal-lenging.Herein,strain-induced strategy is developed to construct the Bi–O-bonded interface in Cu porphyrin-based monoatomic layer(PML-Cu)and Bi_(12)O_(17)Br_(2)(BOB),which triggers the surface interface dual polarization of PML-Cu/BOB(PBOB).In this multi-step polarization,the built-in electric field formed between the interfaces induces the electron transfer from con-duction band(CB)of BOB to CB of PML-Cu and suppresses its reverse migration.Moreover,the surface polarization of PML-Cu further promotes the electron converge in Cu atoms.The introduction of PML-Cu endows a high density of dispersed Cu active sites on the surface of PBOB,significantly promoting the adsorption and activation of CO_(2) and CO desorption.The conversion rate of CO_(2) photoreduction to CO for PBOB can reach 584.3μmol g-1,which is 7.83 times higher than BOB and 20.01 times than PML-Cu.This work offers valuable insights into multi-step polarization regulation and active site design for catalysts.

Molten salt construction of core-shell structured S-scheme CuInS_(2)@CoS_(2) heterojunction to boost charge transfer for efficient photocatalytic CO_(2) reduction

Weak redox ability and severe charge recombination pose significant obstacles to the advancement of CO_(2) photoreduction.To tackle this challenge and enhance the CO_(2) photoconversion efficiency,fabricating well-matched S-scheme heterostructure and establishing a robust built-in electric field emerge as pivotal strategies.In pursuit of this goal,a core-shell structured CuInS_(2)@CoS_(2)S-scheme heterojunction was meticulously engineered through a two-step molten salt method.This approach over the CuInS_(2)-based composites produced an internal electric field owing to the disparity be-tween the Fermi levels of CoS_(2) and CuInS_(2) at their interface.Consequently,the electric field facili-tated the directed migration of charges and the proficient separation of photoinduced carriers.The resulting CuInS_(2)@CoS_(2) heterostructure exhibited remarkable CO_(2) photoreduction performance,which was 21.7 and 26.5 times that of pure CuInS_(2) and CoS_(2),respectively.The S-scheme heterojunc-tion photogenerated charge transfer mechanism was validated through a series of rigorous anal-yses,including in situ irradiation X-ray photoelectron spectroscopy,work function calculations,and differential charge density examinations.Furthermore,in situ infrared spectroscopy and density functional theory calculations corroborated the fact that the CuInS_(2)@CoS_(2) heterojunction substan-tially lowered the formation energy of *COOH and *CO.This study demonstrates the application potential of S-scheme heterojunctions fabricated via the molten salt method in the realm of ad-dressing carbon-related environmental issues.

Advanced semiconductor catalyst designs for the photocatalytic reduction of CO_(2)

Using clean solar energy to reduce CO_(2)into value-added products not only consumes the over-emitted CO_(2)that causes environmental problems,but also generates fuel chemicals to alleviate energy crises.The photocatalytic CO_(2)reduction reaction(PCO_(2)RR)relies on the semiconductor photocatalysts that suffer from high recombination rate of the photo-generated carriers,low light harvesting capability,and low stability.This review explores the recent discoveries on the novel semiconductors for PCO_(2)RR,focusing on the rational catalyst design strategies(such as surface engineering,band engineering,hierarchical structure construction,single-atom catalysts,and biohybrid catalysts)that promote the catalytic performance of semiconductor catalysts on PCO_(2)RR.The advanced characterization techniques that contribute to understanding the intrinsic properties of the photocatalysts are also discussed.Lastly,the perspectives on future challenges and possible solutions for PCO_(2)RR are presented.

Ultrathin origami accordion-like structure of vacancy-rich graphitized carbon nitride for enhancing CO_(2) photoreduction

Retaining the ultrathin structure of two-dimensional materials is very important for stabilizing their catalytic performances.However,aggregation and restacking are unavoidable,to some extent,due to the van der Waals interlayer interaction of two-dimensional materials.Here,we address this challenge by preparing an origami accordion structure of ultrathin twodimensional graphitized carbon nitride(oa-C_(3)N_(4))with rich vacancies.This novel structured oa-C_(3)N_(4) shows exceptional photocatalytic activity for the CO_(2) reduction reaction,which is 8.1 times that of the pristine C_(3)N_(4).The unique structure not only prevents restacking but also increases light harvesting and the density of vacancy defects,which leads to modification of the electronic structure,regulation of the CO_(2) adsorption energy,and a decrease in the energy barrier of the carbon dioxide to carboxylic acid intermediate reaction.This study provides a new avenue for the development of stable highperformance two-dimensional catalytic materials.

Promoting CO_(2) and H_(2)O activation on O-vacancy regulated In-Ti dual-sites for enhanced CH_(4) photo-production

Engineering the specific active sites of photocatalysts for simultaneously promoting CO_(2)and H_(2)O activation is important to achieve the efficient conversion of CO_(2)to hydrocarbon with H_(2)O as a proton source under sunlight.Herein,we delicately design the In/TiO_(2)-VOphotocatalyst by engineering In single atoms(SAs)and oxygen vacancies(VOs)on porous TiO_(2).The relation between structure and performance of the photocatalyst is clarified by both experimental and theoretical analyses at the atomic levels.The In/TiO_(2)-VOphotocatalyst furnish a high CH_(4)production rate up to 35.49μmol g^(-1)h^(-1)with a high selectivity of 91.3%under simulated sunlight,while only CO is sluggishly generated on TiO_(2)-VO.The combination of in situ spectroscopic analyses with theoretical calculations reveal that the VOsites accelerate H_(2)O dissociation and increase proton feeding for CO_(2)reduction.Furthermore,the VOregulated In-Ti dual sites enable the formation of a stable adsorption conformation of In-C-O-Ti intermediate,which is responsible for the highly selective reduction of CO_(2)to CH_(4).This work demonstrates a new strategy for the development of effective photocatalysts by coupling metal SA sites with the adjacent metal sites of support to synergistically enhance the activity and selectivity of CO_(2)photoreduction.

Synthesis of bionic-macro/microporous MgO-modified TiO_2 for enhanced CO_2 photoreduction into hydrocarbon fuels

The stems of water convolvulus were employed as biotemplates for the replication of their optimized 3D hierarchical architecture to synthesize porous MgO-modified TiO2 . The photocatalytic reduction of CO2 with H2O vapor into hydrocarbon fuel was studied with these MgO-TiO2 nanostructures as the photocatalysts with the benefits of improved CO2 adsorption and activation through incorporated MgO. Various factors involving CO2 adsorption capacity, migration of charge carriers to the surface, and the number of activity sites, which depend on the amount of added MgO, determine the photocatalytic conversion efficiency.

Photocatalytic Reduction of Cr^Ⅵ by Natural Sphalerite Suspensions under Visible Light Irradiation

The photocatalytic reductive capability of a natural semiconducting mineral, sphalerite has been studied for the first time. The sphalerite from the Huangshaping deposit of Hunan Province performed great photoreductive capability that 91.95% of the Cr^6＋ was reduced under 9 h visible light irradiation, higher than the 70.58% under 9.5 h UV light irradiation. The highly reductive ability results from its super negative potential of electrons in the conduction band. Furthermore, Fe substitution for Zn introduces donor states, and the oxidation process of Fe^2＋ to Fe^3＋ makes it an effective hole-scavenger. Cd and Cu substitute for Zn also reduce the bandgap and help broaden the absorbing edge towards the visible light. These substituting metal ions in natural sphalerite make it a hyper-active photocatalyst and very attractive for solar energy utilization.

Fabrication of highly dispersed platinum-deposited porous g-C_3N_4 by a simple in situ photoreduction strategy and their excellent visible light photocatalytic activity toward aqueous 4-fluorophenol degradation

A series of highly dispersed platinum‐deposited porous g‐C3N4 (Pt/pg‐C3N4) were successfully fabricated by a simple in situ photoreduction strategy using chloroplatinic acid and porous g‐C3N4 as precursors. Porous g‐C3N4 was fabricated by a pretreatment strategy using melamine as a raw material.The morphology, porosity, phase, chemical structure, and optical and electronic properties ofas‐prepared Pt/pg‐C3N4 were characterized. The photocatalytic activity of as‐prepared Pt/pg‐C3N4was preliminarily evaluated by the degradation of aqueous azo dyes methyl orange under visible light irradiation. The as‐prepared Pt/pg‐C3N4 were further applied to the degradation and mineralization of aqueous 4‐fluorophenol. The recyclability of Pt/pg‐C3N4 was evaluated under four consecutive photocatalytic runs.

Photo-induced transformations of Hg(Ⅱ) species in the presence of Nitzschia hantzschiana,ferric ion,and humic acid

Effects of algae Nitzschia hantzschiana, Fe（Ⅲ） ions, humic acid, and pH on the photochemical reduction of Hg（Ⅱ） using the irradiation of metal halide lamps （λ〉 365 nm, 250 W） were investigated. The photoreduction rate of Hg（Ⅱ） was found to increase with increasing concentrations of algae, Fe（Ⅲ） ions, and humic acid. Alteration of pH value affected the photoreduction of Hg（Ⅱ） in aqueous solution with or without algae. The photoreduction rate of Hg（Ⅱ） decreased with increasing initial Hg（Ⅱ） concentration in aqueous solution in the presence of algae. The photochemical kinetics of initial Hg（Ⅱ） and algae concentrations on the photoreduction of Hg（Ⅱ） were studied at pH 7.0. The study on the total Hg mass balance in terms of photochemical process revealed that more than 42% of Hg（Ⅱ） from the algal suspension was reduced to volatile metallic Hg under the conditions investigated.

Improved charge transfer by size-dependent plasmonic Au on C_3N_4 for efficient photocatalytic oxidation of RhB and CO_2 reduction

A series of Au/g-C3N4(Au/CN)nanocomposites were successfully prepared,where g-C3N4 nanosheets(CN NSs)served as a substrate for the growth of different sized Au nanoparticles(Au NPs)using the constant temperature bath-reduction method.The effect of Au NP size on electron transfer efficiency between the interfaces of the nanocomposite was studied.The three-dimensional finite-difference time-domain results revealed that larger Au NPs showed increased strength of the localized surface plasmon resonance effect.An increased number of high-energy electrons were available for transfer from Au NPs to CN under the visible light irradiation,inhibiting electron transfer from CN to Au NPs.Photoelectrochemical performance analysis showed that smaller Au NPs exhibited higher separation efficiency of the electron-hole pairs photo-generated with reasonable distribution density.These results are favorable for the improvement of photocatalytic performance.Compared to other nanocomposites,the 3-Au/CN sample(prepared using 3 mL HAuCl4 solution)with reasonable distribution density and small Au NPs exhibited the best photodegradation activity(92.66%)of RhB in 30 min under the visible light irradiation and photoreduction performance of CO2 to CO and CH4 with yields of 77.5 and 38.5μmol/g,respectively,in 8 h under UV light irradiation.Considering the experimental results in the context of the literature,a corresponding size-dependent photocatalytic mechanism was proposed.

MgO and Au nanoparticle Co-modified g-C_(3)N_(4)photocatalysts for enhanced photoreduction of CO_(2)with H_(2)O

The photoreduction of CO_(2)to achieve high-value-added hydrocarbons under simulated sunlight irradiation is advantageous,but challenging.In this study,a series of MgO and Au nanoparticle-co-modified g-C_(3)N_(4)photocatalysts were synthesized and subsequently applied for the photocatalytic reduction of CO_(2)with H2O under simulated solar irradiation.The best photocatalytic performance was demonstrated by the Au and 3%MgO-co-modified g-C_(3)N_(4)photocatalysts with CO,CH_(4),CH3OH,and CH3CHO yields of 423.9,83.2,47.2,and 130.4μmol/g,respectively,in a 3-h reaction.We investigated the effects of MgO and Au as cocatalysts on photocatalytic behaviors,respectively.The characterizations and experimental results showed that the enhanced photocatalytic activity was due to the synergistic effect among the components of the ternary photocatalyst.The cocatalyst MgO can activate CO_(2)(adsorbed at the interface between the MgO and Au particles),and the Mg-N bonds formed in the MgO-CN nanosheets played an important role in the charge transfer.Meanwhile,the Au particles that were modified into MgO/g-C_(3)N_(4)can increase the absorption of visible light via the surface plasmon resonance effect and further reduce the activation energies of the photoreduction of CO_(2)using H2O.This study provided an effective method for the modification of traditional primary photocatalysts with promising performance for photocatalytic CO_(2)reduction.

Tunable Syngas Synthesis from Photocatalytic CO2 Reduction Under Visible-Light Irradiation by Interfacial Engineering

Visible-light-driven CO2 photoreduction to achieve renewable materials,such as syngas,hydrocarbons,and alcohols,is a key process that could relieve environmental problems and the energy crisis simultaneously.Reduction of syngas products with diff erent H2:CO proportions is highly expected to produce high value-added chemicals in the industry.However,the development of technologies employing long-wavelength irradiation to achieve CO2 photoreduction and simultaneous tuning of the resultant H2:CO proportion remains a challenging endeavor.In this work,we carried out interfacial engineering by designing a series of heterostructured layered double-hydroxide/MoS2 nanocomposites via electrostatic self-assembly.The syngas proportion(H 2:CO)obtained from CO2 photoreduction could be modulated from 1:1 to 9:1 by visible-light irradiation(λ>400 nm)under the control of the interface-rich heterostructures.This work provides a cost-eff ective strategy for solar-tofuel conversion in an artificial photosynthetic system and describes a novel route to produce syngas with targeted proportions.

Isotype Heterojunction‑Boosted CO_(2) Photoreduction to CO

Photocatalytic conversion of CO_(2) to high-value products plays a crucial role in the global pursuit of carbon–neutral economy.Junction photocatalysts,such as the isotype heterojunctions,offer an ideal paradigm to navigate the photocatalytic CO_(2) reduction reaction(CRR).Herein,we elucidate the behaviors of isotype heterojunctions toward photocatalytic CRR over a representative photocatalyst,g-C_(3)N_(4).Impressively,the isotype heterojunctions possess a significantly higher efficiency for the spatial separation and transfer of photogenerated carriers than the single components.Along with the intrinsically outstanding stability,the isotype heterojunctions exhibit an exceptional and stable activity toward the CO_(2) photoreduction to CO.More importantly,by combining quantitative in situ technique with the first-principles modeling,we elucidate that the enhanced photoinduced charge dynamics promotes the production of key intermediates and thus the whole reaction kinetics.

Supercritical synthesis of platinum-modified titanium dioxide for solar fuel production from carbon dioxide

This paper investigates the properties of TiO2‐based photocatalysts synthesised under supercriticalconditions.Specifically,the characteristics of Pt dispersed on TiO2catalysts obtained in supercriticalCO2are discussed and compared with those of commercial TiO2.The photocatalytic activity of thesynthesised catalysts in the CO2photoreduction reaction to produce solar fuel is tested.The mainconclusion of the study is that photocatalysts with better or similar features,including high surfacearea,crystallisation degree,hydroxyl surface concentration,pore volume,absorbance in the visiblerange and methane production rate,to those of commercial TiO2may be produced for the reductionof CO2to fuel by synthesis in supercritical media.