Utilization Of Charge Carriers Research Articles

Boosting synergistic hole separation and transfer in the TiO2-MXene photoanode by depositing amorphous NiOOH/CoOOH cocatalysts

The efficient separation and transport of photogenerated charge carriers within the photoanode are pivotal for achieving high-performance photoelectrochemical (PEC) water splitting. In this study, TiO2-MXene nanowire arrays (NWAs) adorned with amorphous CoOOH/NiOOH (CN) were fabricated using hydrothermal and photo-assisted electrodeposition techniques. TiO2-MXene-CN NWAs demonstrated a photocurrent density of 1.51 mA/cm2 at 1.23 V versus the reversible hydrogen electrode (vs. RHE), which is 1.46 times and 2.79 times that of TiO2-CN and TiO2, respectively. Electrochemical impedance spectroscopy, photoluminescence, time-resolved photoluminescence, and Mott-Schottky analysis unveiled that the incorporation of MXene and CN substantially augmented the separation of photogenerated electron-hole pairs and efficient charge carrier utilization. Furthermore, the loading of MXene-CN layers ameliorated the light absorption performance of bare TiO2 NWAs. This work provides valuable insights for the design of photoelectrodes employing wide-bandgap materials.

Hole Polaron-Mediated Suppression of Electron-Hole Recombination Triggers Efficient Photocatalytic Nitrogen Fixation.

In the pursuit of successful photocatalytic transformations, challenges persist due to limitations in charge carrier utilization and transfer efficiency, which stemming from rapid recombination. Overcoming these limitations necessitates the exploration of novel mechanisms that enhance the effective separation of photogenerated electron-hole pairs. Herein, deviating from the conventional approach of enhancing carrier migration to separate photogenerated charges and extend their lifetime, the proposal is to directly prevent the recombination of photogenerated electrons and holes by forming hole polarons. Specifically, disordered pores are introduced on the surface of KTaO3 ultrathin sheets, and the clear-cut evidences in electron paramagnetic resonance, photoluminescence, and ultrafast spectroscopy unambiguously confirm the enhanced carrier-phonon coupling, which results in the formation of hole polarons to impede the recombination of photogenerated electron-hole pairs. Taking the challenging nitrogen oxidation reaction as an example, it is found that the hole polarons in atomic-disordered pore KTaO3 ultrathin nanosheets trigger outstanding photo-oxidation performance of nitrogen (N2)to nitrate, with a nitrate-producing rate of 2.1 mg g-1 h-1. This scenario is undoubtedly applicable to a wide variety of photocatalytic reactions due to the common challenge of charge carrier recombination in all photocatalytic processes, manifesting broad implications for promoting photocatalysis performance.

Nanoporous Heterojunction Photocatalysts with Engineered Interfacial Sites for Efficient Photocatalytic Nitrogen Fixation.

Photocatalytic N2 reduction reaction (PNRR) offers a promising strategy for sustainable production of ammonia (NH3). However, the reported photocatalysts suffer from low efficiency with great room to improve regarding the charge carrier utilization and active site engineering. Herein, a porous and chemically bonded heterojunction photocatalyst is developed for efficient PNRR to NH3 production via hybridization of two semiconducting metal-organic frameworks (MOFs), MIL-125-NH2 (MIL=Material Institute Lavoisier) and Co-HHTP (HHTP=2,3,6,7,10,11-hexahydroxytripehenylene). Experimental and theoretical results demonstrate the formation of Ti-O-Co chemical bonds at the interface, which not only serve as atomic pathway for S-scheme charge transfer, but also provide electron-deficient Co centers for improving N2 chemisorption/activation capability and restricting competitive hydrogen evolution. Moreover, the nanoporous structure allows the transportation of reactants to the interfacial active sites at heterojunction, enabling the efficient utilization of charge carriers. Consequently, the rationally designed MOF-based heterojunction exhibits remarkable PNRR performance with an NH3 production rate of 2.1 mmol g-1 h-1, an apparent quantum yield (AQY) value of 16.2% at 365 nm and a solar-to-chemical conversion (SCC) efficiency of 0.28%, superior to most reported PNRR photocatalysts. Our work provides new insights into the design principles of high-performance photocatalysts.

Two-Dimensional High-Entropy Selenides for Boosting Visible-Light-Driven Photocatalytic Performance.

High-entropy materials (HEMs) have garnered extensive attention owing to their diverse and captivating physicochemical properties. Yet, fine-tuning morphological properties of HEMs remains a formidable challenge, constraining their potential applications. To address this, we present a rapid, low-energy consumption diethylenetriamine (DETA)-assisted microwave hydrothermal method for synthesizing a series of two-dimensional high-entropy selenides (HESes). Subsequently, the obtained HESes are harnessed for photocatalytic water splitting. Noteworthy is the optimized HESes, Cd0.9Zn1.2Mn0.4Cu1.8Cr1.2Se4.5, showcasing an output rate of hydrogen of 16.08 mmol h-1 g-1 and a quantum efficiency of ca. 30% under 420 nm monochromatic LED irradiation. It is revealed that the photocatalytic performance of these HESes stems not only from the enlarged specific surface area and enhanced photogenerated charge carrier utilization efficiency but also from the promoted formation of the Cd-Hads bond, influenced by multiple principal elements on the Cd. These findings provide a guide for the design of HEMs tailored for various applications.

Ni-based plasmonic photocatalysts for solar to energy conversion: A review

Plasmonic-based semiconductors are compelling contenders of current research endeavors to drive chemical reactions via plasmonic and phononic light-matter interactions. Among various plasmonic metals, Ni as a non-precious metal has been extensively studied due to its ability to participate in interband excitation and comparable metal-hydrogen binding energy to that of noble metals including Pt and Ag. The phenomenally high charge-carrier density in photoexcited Ni-based plasmonic nanomaterials offers photochemical conversion of high-energy chemical bonds accompanied by thermal effect. Since the research on the plasmonic activity of the non-precious metal is still emerging, no comprehensive review has addressed the significance of Ni as a plasmonic photocatalyst to the best of our knowledge. This review article sums up the recent progress in the field of plasmonic photocatalysis focusing on Ni-based photocatalysts. The basic principles of the plasmonic effect have been presented, along with an explanation of why Ni may be a viable option. Ni has been investigated for use as a co-catalyst and plasmonic photocatalyst in composite photocatalysis to achieve an accelerated process. After the energy transfer mechanism has been assessed, the review covers the state-of-the-art of two significant effects—plasmon energy transfer and the localized heating effect that are responsible for increased efficiency in energy production. In conclusion, we have included a synopsis of the assessment and emphasized the problems that must be resolved before the technology can be made available for purchase. In a nutshell, the chemistry of plasmonic photocatalysis is promising; but acquiring a detailed mechanism of charge transfer and utilization of charge carriers is still a roadblock in apprehending the full potential of plasmonic photocatalysis. Therefore, this study aims to motivate the scientific community to envision impactful work in the creation of next-generation plasmonic photocatalysts.

Profound influence of surface trap states on the utilization of charge carriers in CdS photoanodes

In CdS photoanodes, the decoration of surface sulfur vacancies by CTAB passivates the electron trapping process, resulting in improved photoelectrochemical water oxidation performance.

Efficient photocatalytic hydrogen evolution via interfacial engineering and charge carrier utilization with WSP/g-C3N4 S-scheme heterojunction

The practical implementation of photocatalytic hydrogen generation faces challenges due to the rapid recombination of photogenerated electron-hole pairs. This study reports the synthesis of a WSP/g- C3N4 S-scheme heterojunction catalyst featuring exposed hydrogen evolution active W sites, achieved through in-situ P introducing. Remarkably, the WSP/g-C3N4 catalyst exhibits a superior photocatalytic hydrogen evolution rate of 3.92 mmol h−1 g−1, surpassing g-C3N4 and attaining 112 times the performance of pristine C3N4. A series of characterization techniques and Density functional theory (DFT) reveal that WSP/C3N4 possesses the following advantages as a photocatalyst: 1) Under visible light irradiation, the distinctively ordered and well-crystallized structure generates potential differences, facilitates charge transfers, and enhances the hydrogen evolution activity. 2) The coupling between WSP and g-C3N4 interfaces effectively promotes the directional migration of photogenerated electrons. 3) The shallow bound energy level introduced near the conduction band of WSP effectively prolongs the carrier lifetime. These features collectively contribute to the improved performance of photocatalytic hydrogen evolution. These features collectively contribute to the improved performance of photocatalytic hydrogen evolution. This finding suggests new ways to create organic/inorganic heterojunction composite photocatalysts for efficient hydrogen generation.

Fabrication of graphene modified CeO2/g-C3N4 heterostructures for photocatalytic degradation of organic pollutants

A specific type S-scheme photocatalyst CeO2@N-GO/g-C3N4 was successfully synthesized, resulting in a 2-mercaptobenzothiazole (MBT) degradation rate of 100%, which is more than twice that of g-C3N4 and CeO2. The improved degradation performance can be attributed to the introduction of N-graphene oxide (N-GO), which facilitates the electron transfer. Additionally, the unique Ce4+ → Ce3+ conversion property enhances the charge carrier utilization, and thereby the photocatalytic activity. Furthermore, theoretical calculations suggest the formation of an interfacial internal electric field (IEF) formed between CeO2 (the (200) and (311) planes) and g-C3N4 (the (002) plane) to enhance the delocalization of the charge carriers. Moreover, various photoelectrochemical analyses are employed for the in-depth mechanism on MBT degradation and IEF-induced S-scheme over CeO2@N-GO/g-C3N4, where the differential charge proves the electron transfer path from CeO2 to g-C3N4 that significantly prolongs its lifetime. The radical capture and electron spin resonance (ESR) results proved the existence of the active species of •OH, •O2−, and h+ in the S-scheme photocatalytic system.

Charge transfer mechanism through S-scheme heterojunction in in-situ synthesized TiO2/Fe-doped hydroxyapatite for improved photodegradation of xanthate

The heterojunction structure of the photocatalyst composite, which necessitates a robust interface and sufficient contact areas, holds the key to obtaining high charge carrier migration efficiency. Here, a novel composite, TiO2 nanoparticles/Fe-doped hydroxyapatite (TONPs/FH_CS), is fabricated using a two-step synthetic technique, in which FH_CS is synthesized from artificial converter slag enriched with Fe and Ca. The unique nanorod@plate structure of FH_CS enables the uniform immobilization of TONPs onto FH_CS. Thereby, an n-n type heterojunction exhibits a highly intimate Ti-O-Fe heterointerface. Kelvin probe testing demonstrates the formation of an interfacial electric field oriented from FH_CS to TONPs, which serves as the driving force for interfacial electron transfer through the Ti-O-Fe channels. The photoacoustic signals provide information on electron trap levels and densities, indicating the formation of the electron transfer channels. •O2– and •OH species are responsible for being the active species in this system. A photoexcited carrier transfer pathway exhibiting an S-scheme mechanism with high separation efficiency significantly enhances the utilization of charge carriers in each phase. Thus, improved xanthate degradation has been achieved using a heterojunction containing a photocatalyst derived from industrial solid waste. This work demonstrates the significant potential of steel-making byproduct utilization in industrial wastewater treatment.

Cs3Bi2Br9/BiOBr S-scheme heterojunction for selective oxidation of benzylic C[sbnd]H bonds

Converting hydrocarbons into aldehydes in a green and environmentally benign way is of great significance in fine chemistry. In this work, all-inorganic Cs3Bi2Br9 perovskite nanoparticles were uniformly loaded on BiOBr nanosheets via an in-situ growth method, which can selectivity photoactivate aromatic C(sp3)H bond of toluene to generate benzaldehyde. According to the in-situ X-ray photoelectron spectroscopy characterization, the photogenerated electrons of BiOBr transfer to Cs3Bi2Br9 enforced by the internal electric field under light irradiation, resulting in S-scheme heterojunction. Furthermore, theoretical calculations indicate that toluene molecules are inclined to adsorb on the BiOBr surface, subsequently involving the oxidation reaction to generate benzyl radical (PhCH2•) by using the energetic holes of BiOBr, while the remaining photoinduced electrons in the conduction band (CB) of Cs3Bi2Br9 with powerful reduction ability reduce O2 into •O2−, which is the vital oxidative active species working on toluene selective oxidation process. Such an unexceptionable charge carrier utilization mode and tendentious adsorption behavior of reactants contribute to the optimized Cs3Bi2Br9/BiOBr heterojunction with excellent photocatalytic performance, achieving a maximum of 22.5% toluene conversion and 96.2% selectivity towards benzaldehyde formation. This work provides a rational photocatalyst heterojunction construction protocol for the selective oxidation of saturated aromatic CH bonds.

Heterostructured CoFe1.5Cr0.5S3O/COFs/BiVO4 photoanode boosts charge extraction for efficient photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting can convert the inexhaustible solar energy into green and storable H2 to tackle fossil crisis and meet carbon neutrality. BiVO4 is regarded as a promising photoanode owing to its superior visible light absorption, moderate redox potentials and well chemical stability, but suffering from the rapid recombination of charge carriers and sluggish interfacial water oxidation kinetics. Herein, a heterostructured CoFe1.5Cr0.5S3O/COFs/BiVO4 photoanode was fabricated to accelerate charge carriers′ separation and boost water oxidation. The spinel-type CoFe1.5Cr0.5S3O serving as the co-catalyst enabled to largely lower the overpotential of water oxidation, while COFs acting as an interlayer passivated the interfacial defect between CoFe1.5Cr0.5S3O and BiVO4. Benefiting from the collaboration of CoFe1.5Cr0.5S3O co-catalyst and COFs interlayer, heterostructured CoFe1.5Cr0.5S3O/COFs/BiVO4 photoanode featuring with a prominent charge extraction efficiency reached an impressive water oxidation photocurrent of 5.1 mA cm−2 at 1.23 V vs. RHE under AM 1.5 G irradiation, higher than that of pristine BiVO4, binary COFs/BiVO4 and CFCOS/BiVO4 photoanodes. This work demonstrated that heterostructured BiVO4-based photoanode with co-catalyst and interlayer enables to simultaneously enhance charge carrier utilization efficiency and optimize surface catalysis kinetics for efficient solar-to-fuel conversion.

Promoted Utilization of Charge Carriers in La5Ti2Cu0.9Ag0.1O7S5-Based Photocatalyst Sheets for Efficient Z-Scheme Overall Water Splitting

Promoting charge separation and redox reaction kinetics of semiconductor photocatalysts are crucial for enhancing the performance of overall water splitting (OWS). However, it is rather challenging for narrow bandgap photocatalysts due to the severe charge recombination and decreased driving force. The present work demonstrates that efficient utilization of charge carriers on La5Ti2Cu0.9Ag0.1O7S5 (LTCA), an oxysulfide photocatalyst having an absorption edge of 650 nm, can be achieved for Z-scheme OWS via Ga-doping and Rh cocatalyst deposition in a two-step strategy. Ga-doping of LTCA promoted charge separation, and the developed Rh cocatalyst loading over LTCA:Ga created catalytic sites with high dispersion and less aggregation, leading to improved charge transfer and catalytic conversion. An apparent quantum yield of 11.8% at 420 nm was achieved over the assembled cocatalyst-loaded LTCA:Ga|Au|BiVO4:Mo Z-scheme OWS system, which was the highest among OWS systems involving photocatalysts utilizing photons with wavelengths longer than 600 nm.

Atomically precise AuxAg25-x nanoclusters with a modulated interstitial Au-Ag microenvironment for enhanced visible-light-driven photocatalytic hydrogen evolution.

Herein, we report the study of atomically precise AuxAg25-x nanoclusters (NCs) toward photocatalytic hydrogen evolution. The incorporation of Au atoms into Ag25 NCs not only narrowed the HOMO-LUMO gaps but also created an interstitial Au-Ag microenvironment, which promoted the photogenerated charge carrier utilization and optimized the reaction dynamics.

Frontispiece: Effective Charge Carrier Utilization of BiVO4 for Solar Overall Water Splitting

The current research status of BiVO4-constituted photo(electro)catalytic systems for solar overall water splitting (OWS) is reviewed in this paper. Herein, effective charge carrier utilization is illustrated as the mainline, in which charge separation, charge transfer and surface catalytic reaction are detailly summarized towards the construction of efficient solar OWS systems. More information can be found in the Review article by S. Chen, F. Zhang et al. (DOI: 10.1002/chem.202201812

Effective Charge Carrier Utilization of BiVO4 for Solar Overall Water Splitting.

Solar energy-driven overall water splitting (OWS) is an attractive way for generating clean and renewable green hydrogen. One key challenge is the construction of OWS systems with high solar energy conversion efficiencies, in which how to manipulate photoexcited charge carriers to efficiently participate in the reaction is the top priority. In recent years, bismuth vanadate (BiVO4 ) has emerged as one of the most promising materials for photo(electro)catalytic OWS and considerable progress has been achieved. In this review, recent advances of BiVO4 -constituted OWS systems in both photoelectrocatalytic and photocatalytic approaches are presented in a mainline of effective charge carrier utilization. Various strategies for improved charge carrier utilization, including band structure engineering, improving charge separation, reducing charge recombination, and accelerating reaction kinetics, are summarized and analyzed in detail. Finally, perspective and outlook on further exploring the application potential of BiVO4 are proposed.

Influence of Wurtzite ZnO Morphology on Piezophototronic Effect in Photocatalysis

A piezoelectric field promotes the photocatalytic activity of a photocatalyst by helping separating photo-generated charge carriers. Wurtzite phase ZnO is a typical photocatalyst with a piezoelectric property, thus self-assisted photocatalysis with ZnO based on the piezophototronic effect can be achieved. ZnO nanorods or nanowires with a clear c-axis have been well studied, while other morphologies have not been fully discussed. In this work, we prepared wurtzite phase ZnO with four different morphologies. By comparing their photocatalytic activity for degradation of Rhodamine B under the same mechanical energy source provided by ultrasound, the effect of morphology and exposed facets on photo-induced charge separation were highlighted. The ZnO nanowire photocatalyst delivered an impressive improvement in photocatalytic efficiency when ultrasound driven, suggesting that the morphology-related piezophototronic effect had a positive effect on separation of photo-generated charge carriers, and more exposed active facets benefitted the utilization of charge carriers.

Plasmonic Photocatalysis: Activating Chemical Bonds through Light and Plasmon

AbstractThe exceptionally large charge‐carrier density in photoexcited plasmonic nanoparticles (NPs) can be used for the making and breaking of high‐energy chemical bonds, which forms the basis of plasmonic photocatalysis. This review showcases the roadmap of important events and major bottlenecks in plasmonic photocatalysis, along with highlighting a few probable solutions for achieving the desired targets. The review starts with a discussion on various excitation and relaxation pathways, followed by the section on initial use of plasmons in enhancing the photocatalytic properties of semiconductor materials. Next, the sole use of plasmonic NPs in driving useful and industrially relevant chemical transformations is discussed. This is followed by a critical assessment of various challenges and opportunities in the area, along with a discussion on emerging experiments capable of overcoming these challenges. Decades of research have provided a clear understanding on charge generation and decay processes in plasmonic NPs. However, achieving an efficient separation and utilization of charge carriers is still a roadblock in realizing the full potential of plasmonic NPs in catalysis. In short, doing chemistry with plasmons is attractive; but it is high time to develop strategies that can quantitatively utilize the charge carriers for driving chemical transformations in a selective and efficient way.

Regulating interfacial morphology and charge-carrier utilization of Ti3C2 modified all-sulfide CdS/ZnIn2S4 S-scheme heterojunctions for effective photocatalytic H2 evolution

The separation efficiency of electrons and holes and the enhancement of the surface reductive reaction in the metal sulfide semiconductor photocatalysts are important factors in boosting photocatalytic H2 evolution from water. The control of both interface morphology and the charge–carrier utilization of metal sulfide-based photocatalysts can effectively improve the separation efficiency of electrons and holes and increase the surface reaction active sites, which are considered to be effective methods to improve the photocatalytic activity of semiconductors. Here, the Ti3C2 (Mxene) modified all-sulfide 2D/2D S-scheme heterojunction Ti3C2/ ZnIn2S4(ZIS)/CdS composite material was firstly synthesized by a two-step solvothermal method. The formation of all-sulfide S-scheme heterojunction improves the efficiency of electron-hole separation. The intimate 2D/2D van der Waals structure provides a strong interaction force and a large contact area to enhance charge transfer. The addition of 2D Ti3C2 forms the accumulation layer, reducing the recombination of electrons and holes. Under the synergistic promotion, the highest hydrogen production of the prepared Ti3C2/ZIS/CdS composite photocatalyst could reach 8.93 mmol/h/g. This work not only enriches the photocatalytic systems through integrating the ohmic junction and the 2D/2D all-sulfide S-scheme heterojunction, but also provides a satisfactory design strategy for engineering interfacial morphology and charge-carrier utilization.

Facile construction of CoO/Bi2WO6 p-n heterojunction with following Z-Scheme pathways for simultaneous elimination of tetracycline and Cr(VI) under visible light irradiation

Developing low-cost, efficient and sustainable utilization of visible light catalysts to eliminate antibiotic and heavy metals contaminants simultaneously remains a huge challenge. Herein, a unique CoO/Bi2WO6 p-n heterojunction was successfully synthesized by a facile and simple solvothermal method for simultaneous elimination of tetracycline and Cr(VI) under visible light irradiation. Benefiting from p-n heterojunction following Z-Scheme pathways, 30 wt% CoO/Bi2WO6 heterojunction displayed the best photocatalytic activity for tetracycline degradation (90.7%) and Cr(VI) reduction (57.5%) singly after 90 min reaction. The reaction rate constant for CoO/Bi2WO6 heterojunction towards tetracycline degradation and Cr(VI) reduction were 0.02607 min−1 and 0.00909 min−1, which are 4.23, 4.92 times of pure CoO and 3.46, 4.61 times of pure Bi2WO6, respectively. It is related to the formation of p-n heterojunction, which avoids the agglomeration induced inactivation, extends the spectral response and facilitates the separation and utilization of charge carriers. More interestingly, the higher photocatalytic efficiencies are achieved to simultaneously eliminate the mixed tetracycline and Cr(VI), which are 1.03 and 1.76 times that of single tetracycline and Cr(VI), respectively. Moreover, the 30 wt% CoO/Bi2WO6 heterojunction photocatalyst can be reused for ten cycles and exhibits satisfactory properties of stableness and reusability. Furthermore, the possible reaction pathway and photocatalytic mechanism for TC degradation and Cr(VI) reduction were revealed based on capturing experiments of active species, electron spin resonance and liquid chromatography mass spectrometry. These findings provide a great promise of CoO/Bi2WO6 p-n heterojunction photocatalyst in mixed contaminants remediation.

Aligning potential differences within carbon nitride based photocatalysis for efficient solar energy harvesting

Photocatalysis is essentially triggered by the photoinduced charge carriers, which are then oriented for the targeted redox reactions. However, the effects of intrinsic driving forces on charge carriers and their resulting photocatalytic throughputs remain unclear. Herein, we focus on two main potential differences (PDs), e.g., intralayer PD (IPD) within two-dimensional carbon nitride hybrids, and band PD (BPD) between the band positions of a semiconductor and the redox potentials of reactants that can actuate charge carriers for photocatalysis. In situ experiments and theoretical computations identify and differentiate the roles of the two PDs on the separation, transportation and catalytic utilization of charge carriers. It is noteworthy that the enhancement from PDs alignment in this work is higher than other physiochemical modifications (e.g., mass transfer and polymerization degree) for photocatalysis. This study may offer a guiding principle for aligning a photocatalyst with target reactions for energy conversion and chemical synthesis. • Intralayer potential difference (IPD) and band PD (BPD) within carbon nitride based photocatalysis were both engineered. • The individual contribution of IPD and BPD to governing the charge carriers was clearly illustrated. • The interaction between IPD and BPD on the throughput of different photocatalytic systems was unveiled. • Enhancement from PDs alignment was higher than that via modifications of other physiochemical properties of catalyst.