High Charge Carrier Recombination Research Articles

Surface ion-exchange induced Bi-rich Bi12O17Cl2/BiOCOOH/Bi2MoO6 heterojunction with oxygen vacancies for enhanced photocatalytic nitrogen fixation

Photocatalytic nitrogen reduction presents a promising technology for environmentally friendly ammonia synthesis under mild conditions. However, the performance of photocatalysts is often hindered by high charge carrier recombination and insufficient adsorption and activation of nitrogen molecules. A novel Bi12O17Cl2/BiOCOOH/Bi2MoO6 heterojunction photocatalyst was successful synthesis through surface ion-exchange technique by potassium chloride. The introduction of Bi-rich Bi12O17Cl2 on BiOCOOH/Bi2MoO6 heterojunction not only improves electron transfer efficiency due to the dual type-II heterojunction effect but also facilitates on-site N2 adsorption and activation for solar ammonia production by promoting oxygen vacancies. The high photocatalytic nitrogen fixation activity of the Bi12O17Cl2/BiOCOOH/Bi2MoO6 was 107.78 μmol g−1 h−1 without any sacrificial agent. DFT calculations indicate that oxygen vacancies serve as the active site for adsorbed N2, the hydrogenation process preferentially forms on the distal N2 atom with a lower activation energy about 0.6 eV. Therefore, the combination of oxygen vacancies and band engineering accelerates the production of ammonia. This endeavor holds the potential to unleash the capabilities of engineering for Bi-rich heterojunctions materials with oxygen vacancies, thereby achieving high-efficiency solar-driven N2-to-NH3 conversion in aqueous environments.

Engineering of g-C3N4 for Photocatalytic Hydrogen Production: A Review.

Graphitic carbon nitride (g-C3N4)-based photocatalysts have garnered significant interest as a promising photocatalyst for hydrogen generation under visible light, to address energy and environmental challenges owing to their favorable electronic structure, affordability, and stability. In spite of that, issues such as high charge carrier recombination rates and low quantum efficiency impede its broader application. To overcome these limitations, structural and morphological modification of the g-C3N4-based photocatalysts is a novel frontline to improve the photocatalytic performance. Therefore, we briefly summarize the current preparation methods of g-C3N4. Importantly, this review highlights recent advancements in crafting high-performance g-C3N4-based photocatalysts, focusing on strategies like elemental doping, nanostructure design, bandgap engineering, and heterostructure construction. Notably, sophisticated doping techniques have propelled hydrogen production rates to a 104-fold increase. Ingenious nanostructure designs have expanded the surface area by a factor of 26, concurrently extending the fluorescence lifetime of charge carriers by 50%. Moreover, the strategic assembly of heterojunctions has not only elevated charge carrier separation efficiency but also preserved formidable redox properties, culminating in a dramatic hundredfold surge in hydrogen generation performance. This work provides a reliable and brief overview of the controlled modification engineering of g-C3N4-based photocatalyst systems, paving the way for more efficient hydrogen production.

Nitrogen‐Rich Carbon Nanodot‐Sensitized TiO2 with MWCNT Composites for Efficient Visible Light Photocatalysis

AbstractTiO2‐based composite photocatalysts are currently being explored to address concerns intrinsic to TiO2, specifically high charge carrier recombination and UV light activation. Among various materials utilized for composite formation, carbon nanomaterials stand out due to their high electron conductivity, charge storage, photosensitization, and surface properties. However, high carbon content in composites has been shown to reduce performance with potential toxicity concerns. To harness the diverse properties of carbon nanomaterials in a single composite while optimizing the carbon content below 1% by weight, multi‐walled carbon nanotubes (MWCNT)/TiO2 sensitized by carbon nanodots (CND) are synthesized. The heterojunction formed between MWCNTs and TiO2 in the binary composite reduced the charge carrier recombination rate compared to TiO2. The addition of CNDs to MWCNT/TiO2 induced visible light absorbance of the resulting ternary composite, due to the forbidden electron transitions undergone in CND aggregates. CND/MWCNT/TiO2 exhibited a fivefold and 1.6‐fold increase in photocatalytic degradation of acid orange 7 and tetracycline under visible light compared to TiO2. This enhancement is attributed to the photosensitizing property of CNDs working in synergy with the charge storage ability of MWCNTs. A plausible charge transfer pathway for the activity of CND/MWCNT/TiO2 is proposed.

Electrospinning mediated solvothermal preparation of hierarchical MGa2O4/ZnIn2S4 (M = Ni, Co) hollow nanofibers with p-n heterojunction for boosting photocatalytic H2 evolution

ZnIn2S4 has been extensively studied in the field of photocatalytic hydrogen evolution (PHE), but its bulky structure often results in high charge carrier recombination and low light harvesting capability. Herein, efficient hierarchical MGa2O4/ZnIn2S4 (M = Ni, Co) hollow nanofiber photocatalysts with p-n heterojunction were fabricated by an electrospinning-solvothermal method. The hierarchical structure of MGa2O4/ZnIn2S4 composites has facilitated p-n heterojunction formation, promoted the charge separation efficiency, enhanced light harvesting capability, and provided abundant reactive sites. The synergistic effects of MGa2O4 and ZnIn2S4 accelerated the PHE rate by reducing the *H reaction intermediates energy barrier. Under simulated solar light, the NiGa2O4/ZnIn2S4 and CoGa2O4/ZnIn2S4 with optimal proportions delivered outstanding PHE rate of 9292 and 6283 µmol·g−1·h−1, which was 5 and 3 times higher than that of pure ZnIn2S4, respectively. This work opens up an efficient electrospinning-mediated solvothermal strategy for constructing hierarchical ZnIn2S4-based nanofiber composites with excellent PHE performance.

Effect of ball milling time on Sr0.7Sm0.3Fe0.4Co0.6O2.65 perovskites and their application as semiconductor layers in dye-sensitized solar cells

The practical utilization of TiO2 as a semiconductor in dye-sensitized solar cells (DSSCs) has been set back by poor visible light absorption, high charge carrier recombination, and low electrical conductivity, which reduce the power conversion efficiency (PCE) and sustainability of the device. In this respect, perovskites with excellent properties, such as large surface area, good optical properties, high electrical conductivity, and superior electrochemical stability, have recently emerged as promising alternatives capable of overcoming the drawbacks of TiO2. Herein, Sr0.7Sm0.3Fe0.4Co0.6O2.65 (SSFC) perovskites were prepared via the ball milling method at various milling times of 0, 5, and 10 h, and the obtained samples were denoted by SSFC-0, SSCF-5, and SSCF-10, respectively. Increasing the ball milling time led to a significant reduction in nanoparticle size and agglomeration, which, in turn, increased the surface area and electrical conductivity of the samples. As a consequence, the SSFC-10 perovskite exhibited the smallest average particle sizes (18.9 nm) with the largest surface area (61.8 m2 g−1) and minimum defects, which allowed for efficient electron transport, resulting in the best electrical conductivity of 49.8 S cm−1. Ultimately, DSSCs fabricated using SSFC-10 semiconductor layers achieved an optimum PCE of 6.01 %, which is an improvement of 8.67 %, 1.1 %, and 6.56 % for SSFC-0 (3.69 %), SSFC-5 (4.96 %), and TiO2 (5.64 %), respectively. Thus, varying the ball milling time can be used as an effective technique to tailor the physicochemical properties of SSFC to suit desired applications, particularly the fabrication of highly efficient and sustainable DSSC semiconductor layers.

Large-area phosphorene for stable carbon-based perovskite solar cells

Carbon-based perovskite solar cells (c-PSCs) have attracted increasing attention due to their numerous advantages including ease of fabrication, the potential of assembling flexible devices, low manufacturing costs as well as large-scale production. However, c-PSCs suffer from the limited hole extraction and high charge carrier recombination due to the inadequate interface contact between the carbon electrode and perovskite film. Herein, we report the fabrication of planar c-PSCs with high efficiency and excellent stability by employing electrochemically produced large-area phosphorene flakes as a hole-transporting layer (HTL). Large-area phosphorene shows well-aligned band energy levels with the perovskite, and thus led to the efficient hole extraction and the reduced hysteresis behaviour. Consequently, while exhibiting excellent stability under various harsh testing conditions, the devices with phosphorene HTL delivered a power conversion efficiency of over 15% with an open-circuit voltage of 1.082 V, which is the highest reported value for c-PSCs without traditional hole transporting materials to date.

Bi/BSO Heterojunctions via Vacancy Engineering for Efficient Photocatalytic Nitrogen Fixation

AbstractPhotocatalytic nitrogen reduction represents a viable technology for green ammonia synthesis under mild conditions. However, the performance of the photocatalysts is typically limited by high charge carrier recombination and low adsorption and activation of nitrogen molecules. Herein, Bi/Bi2Sn2O7 (Bi/BSO) heterojunction nanocomposites are prepared via a one‐step hydrothermal method, where NaOH etching of oxygen vacancies in the Bi─O bonds of Bi2Sn2O7 (BSO) is exploited for the in situ formation of metallic Bi and hence Schottky junctions with the semiconducting BSO. This leads to a high separation rate of photogenerated charge carriers. Consequently, compared to the pure‐phase BSO, the Bi/BSO heterostructures exhibit markedly enhanced ammonia production, reaching an optimum rate of 284.5 µmol g−1 h−1, where the rectifying contact between the semiconducting BSO and metallic Bi facilitates directional BSO to Bi electron transfer, leading to enrichment of photogenerated electrons at the active sites of metallic Bi. First‐principles calculations confirm the alteration of active sites and the guided electron flow by the Schottky junctions and surface oxygen vacancies. Results from this study offer an effective paradigm of structural engineering in manipulating the photocatalytic activity of bismuth‐based pyrochlore materials toward nitrogen fixation to ammonia.

Anthracene-based dual channel donor-acceptor triazine-containing covalent organic frameworks for superior photoelectrochemical sensing

Covalent organic frameworks (COFs) exhibit excellent photoelectrically active structures and serve as channels for photon capture and charge carrier transport. However, their relatively high charge-carrier recombination rates and lack of specific recognition sites limit their application in photoelectrochemical sensing. This paper reports a functionalized donor–acceptor (D-A) COF comprising electron-rich polycyclic aromatic moieties and electron-deficient triazines (Tz) incorporating boronic acid through ligand exchange. The number of aromatic rings in the polycyclic aromatic moiety is crucial for establishing an efficient D-A system within COF. In the absence of an external electron donor, the anthracene-based COF exhibited a five-fold enhancement in photocurrent compared to the naphthalene-based COF. The resulting anthracene-based D-A COF exhibited enhanced orbital overlap and electron push–pull interactions, facilitating more effective charge separation. Furthermore, introducing boronic acid enabled the selective enrichment of low-concentration external electron donors, such as dopamine, in the inner Helmholtz plane. This ingenious approach establishes a unique dual-channel D-A system that allows direct measurement of dopamine in serum. Under optimized conditions, the test platform achieves good correspondence for dopamine at 1 to 100 nM and 0.5 to 100 μM with a detecting limit of 0.36 nM (3σ/S, n = 11). This strategy introduces a novel dimension to photoelectrochemical sensing, focusing on the effect of spatial separation between the external electron donor and the photoelectrode interface that intricately shapes the behavior and enhances the performance of the photoelectric system.

Interfacial engineering of a multijunctional In2O3/WO3@Ti4N3Tx S-scheme photocatalyst with enhanced photoelectrochemical properties.

Achieving high photoelectrochemical conversion efficiency requires the logical layout of a composite photocatalyst with optimal charge separation and transfer with ideal light harvesting capabilities to enhance the photocatalytic performance and the degradation rate towards organic pollutants. Herein, a novel In2O3/WO3@Ti4N3Tx S-scheme heterojunction was successfully synthesized and confirmed through valence band VB-XPS and Mott Schottky combined analysis. The formed MXene-doped In2O3/WO3@Ti4N3Tx S-scheme significantly enhances the charge flow and spatial separation with an improved oxidation and reduction ability. An in-built interfacial electric field at the WO3-In2O3 boundary enhanced the light-harvesting capacity, whereas Ti4N3Tx MXene offers a unique electron trapping effect which effectively lowers high charge carrier recombination rate-related photocatalytic deficit. It preserves the exceptional redox potency of the photocatalyst by providing a directed acceleration and effective separation of the photogenerated charges. A high carrier density (ND = 7.83 × 1021 cm-3) with a lower negative flat band (VFB = -0.064 V vs. Ag/AgCl) was obtained by Mott-Schottky analysis for 3 wt% In2O3/WO3@Ti4N3Tx, an indicator that a low overpotential is needed to activate photocatalytic reactions. This study, therefore, provides a novel thought for the design and fabrication of an S-scheme heterojunction for photocatalytic reactions for mineralization of organic pollutants in water and clean energy production.

Unveiling the Influence of Sulfur Doping on Photoelectrochemical Performance in BiVO4/FeOOH Heterostructures.

BiVO4 is a promising photoanode for photoelectrochemical (PEC) water splitting but suffers from high charge carrier recombination and sluggish surface water oxidation kinetics that limit its efficiency. In this work, a model of sulfur-incorporated FeOOH cocatalyst-loaded BiVO4 was constructed. The composite photoanode (BiVO4/S-FeOOH) demonstrates an enhanced photocurrent density of 3.58 mA cm-2, which is 3.7 times higher than that of the pristine BiVO4 photoanode. However, the current explanations for the generation of enhanced photocurrent signals through the incorporation of elements and cocatalyst loading remain unclear and require further in-depth research. In this work, the hole transfer kinetics were investigated by using a scanning photoelectrochemical microscope (SPECM). The results suggest that the incorporation of sulfur can effectively improve the charge transfer capacity of FeOOH. Moreover, the oxygen evolution reaction model provides evidence that S-doping can induce a "fast" surface catalytic reaction at the cocatalyst/solution interface. The work not only presents a promising approach for designing a highly efficient photoanode but also offers valuable insights into the role of element doping in the PEC water-splitting system.

Decoration of silver on ZnS for enhancement of sunlight-driven photodegradation of reactive red azo dye and norfloxacin antibiotic

High charge carrier recombination rate is the major difficulty affecting low photocatalytic performance of the UV-responsive ZnS photocatalyst. To overcome the problem, well dispersion of noble metals on the ZnS surface can be regarded as one of the useful strategies to enhance the photocatalytic efficiency. This is due to a synergy of creation of heterojunction structure and surface plasmon resonance effect. In the present work, the surface of the hydrothermally grown ZnS photocatalyst was modified with 10 wt %silver. The hexagonal Ag/ZnS photocatalyst provided high sunlight-active photocatalytic performance toward removal of anionic azo dye and norfloxacin antibiotic with the efficiency of about 99 % and 70 %, within 120 min, respectively. The improvement of the resultant photoactivity is attributed to increasing of charge separation capacity at the interface. Well distribution of silver on ZnS surface results in the generation of the Schottky barrier at the Ag/ZnS interface. This will end up with the increment of quantum efficiency and enlargement of the photocatalytic activity. Additionally, after modification of ZnS surface by addition of silver, a red shift in the light absorption toward visible region was found. This is assigned to the effect of surface plasmon resonance (SPR) of Ag on ZnS surface. The synthesized Ag/ZnS reveals high structural stability with enhanced performance even after the fifth cycle. This work demonstrates a new avenue for creation of a silver-modified ZnS for complete degradation of toxic organic contaminants including dyes and antibiotics by use of the abundant solar energy.

Internal Electric Field and Adsorption Effect Synergistically Boost Carbon Dioxide Conversion on Cadmium Sulfide@Covalent Triazine Frameworks Core–Shell Photocatalyst

AbstractSolar‐driven photocatalytic conversion of carbon dioxide (CO2) into carbon‐neutral fuels is of significance for energy sustainability. The critical challenges in this process are high charge carrier recombination and low CO2 adsorption capacity. Here, by integrating porous covalent triazine frameworks (CTFs) with cadmium sulfide (CdS) nanospheres, a CdS@CTF‐HUST‐1 heterojunction photocatalyst with core–shell structure is developed for CO2‐to‐CO conversion. Experimental investigations combined with density functional theory simulations reveal that the formation of an internal electric field provides the driving force for accelerating S‐scheme charge transfer, resulting in enhanced separation and utilization efficiency of charge carriers in photocatalysis. Together with the improved CO2 adsorption capacity contributed by the porous structure of the CTF‐HUST‐1 shell, the CdS@CTF‐HUST‐1 heterojunction photocatalyst gives an impressive CO yield rate of 168.77 µmol g−1 h−1 with high selectivity. This research furnishes a feasible strategy to construct highly active core–shell composite photocatalysts for optimizing CO2 adsorption and conversion.

Single-atom Nb anchored on graphitic carbon nitride for boosting electron transfer towards improved photocatalytic performance

Single-atom Nb anchored on g-C3N4 was prepared by facile thermal polymerization. Compared with pure g-C3N4, optimized Nb-anchoring samples exhibited excellent CO and CH4 yield and higher photocatalytic oxidation efficiency in degrading amoxicillin (AMX). Combining DFT calculations and experimental results, the enhanced photocatalytic performance was attributed to anchored single-atom Nb in terms of Nb-C and the formation of N defects. Anchoring with single-atom Nb contributed to the formation of N defects in g-C3N4, inducing the formation of polarized Nb-C bonds with high conductivity accelerating the directional transfer of photogenerated electrons and holes. Moreover, this restrained the relatively high charge carrier recombination rate of g-C3N4. Additionally, N defects with solitary electrons could enhance the charge density and serve as active centers for a photocatalytic reaction. The present work underlines the importance of the synergistic effect of anchoring Nb and simultaneously generating N defects for developing a new generation of g-C3N4-based photocatalysts.

π-Conjugated In-Plane Heterostructure Enables Long-Lived Shallow Trapping in Graphitic Carbon Nitride for Increased Photocatalytic Hydrogen Generation.

The relatively short-lived excited states, such as the nascent electron-hole pairs (excitons) and the shallow trapping states, in semiconductor-based photocatalysts produce an exceptionally high charge carrier recombination rate, dominating a low solar-to-fuel performance. Here, a π-conjugated in-plane heterostructure between graphitic carbon nitride (g-CN) and carbon rings (Crings ) (labeling g-CN/Crings ) is effectively synthesized from the thermolysis of melamine-citric acid aggregates via a microwave-assisted heating process. The g-CN/Crings in-plane heterostructure shows remarkably suppressed excited-state decay and increased charge carrier population in photocatalysis. Kinetics analysis from the femtosecond time-resolved transient absorption spectroscopy illustrates that the g-CN/Crings π-conjugated heterostructure produces slower exciton annihilation (τ1 = 7.9ps) and longer shallow electron trapping (τ2 = 407.1ps) than pristine g-CN (τ1 = 3.6ps, τ2 = 264.1ps) owing to Crings incorporation, both of which enable more photoinduced electrons to participate in the photocatalytic reactions, thereby realizing photoactivity enhancement. As a result, the photocatalytic activity exhibits an eightfold enhancement in visible-light-driven H2 generation. This work provides a viable route of constructing π-conjugated in-plane heterostructures to suppress the excited-state decay and improve the photocatalytic performance.

Microwave-Assisted Hydrothermal Synthesis of Fe-Doped TiO2 Photoanode for Photocatalytic Hydrogen Evolution

One-dimensional TiO2 nanostructures like nanotubes, nanowires, and nanorods have received huge attention due to their photocatalytic hydrogen-generating ability. However, its wide band gap and high charge carrier recombination rate hampered the efficiency with which it converts solar energy into hydrogen. To improve this application, metallic doping employing a quick and easy synthesis method should be proposed. In this study, we report on the microwave-assisted hydrothermal synthesis of iron-doped TiO2 nanowires on an FTO substrate. The formation of TiO2 nano-wires was validated by structural and morphological analysis carried out using XRD and SEM imaging respectively. EDX was employed to provide a breakdown of their chemical composition to verify the presence of dopants in the samples. The impact of Fe-doping on optical and photoelectrochemical properties was studied. Electrochemical impedance spectroscopy was used to determine the mechanisms behind charge accumulation and charge transfer properties. The Mott-Schottky plot was used to examine the donor density and the flat-band potential of the pristine and Fe-doped TiO2 samples.

Plasmonic Ag-nanoparticles decorated phosphorus and boron co-doped g-C3N4 for enhanced photocatalytic H2 production

Solar water splitting by semiconductor photocatalysts has emerged as a favorable approach for green hydrogen production. Graphitic carbon nitride (g-C3N4) has gained substantial recognition amongst numerous semiconductor photocatalysts as a metal-free semiconductor with suitable band gap, appropriate band edge positions, and satisfactory photocatalytic activity for hydrogen production. However, its practical application is severely affected by high charge carrier recombination rate and inefficient visible light absorption. Introducing non-metal dopants into the g-C3N4 structure could suppress charge carrier recombination and tune the electronic property. Also, metal nanoparticles exhibit surface plasmon resonance (SPR) upon light interaction increasing the visible light absorption by the transport of hot electrons into the g-C3N4 framework. In this work, we report hybrid photocatalytic materials containing Ag-plasmonic metal and non-metal (B/P) dual heteroatom-doped g-C3N4 prepared via in-situ thermal polycondensation and succeeded by the photodeposition of Ag NPs. The structure of the prepared materials was studied through PXRD and FTIR spectroscopy; XPS was used for chemical analysis; SEM was used to study the morphology; and optical characteristics were studied through UV–Vis and PL spectroscopic techniques. The synergistic effects of SPR and heteroatom co-doping exhibit superior photocatalytic hydrogen production compared to pristine, B or P individual-doped, and B/P co-doped g-C3N4 samples. The optimized 1Ag/PBCN photocatalyst has demonstrated the highest photocatalytic hydrogen production rate of 1825 μmolh-1g−1, 18.3 times greater than g-C3N4. The modified hybrid material shows better activity due to the efficient charge carriers separation and extended visible light absorption. This work indicates that elemental co-doping and loading plasmonic nanoparticles on g-C3N4 to form hybrid nanocomposites may be a potential strategy to achieve better photocatalytic hydrogen evolution. The proposed methodology and outcomes will be helpful in the design and development of plasmon-enhanced hybrid photocatalysts for solar-driven green hydrogen production from water splitting.

Constructing spike-like energy band alignment at the heterointerface in highly efficient perovskite solar cells.

The interface between the absorber and transport layers is shown to be critical for highly efficient perovskite solar cells (PSCs). The undesirable physical and chemical properties of interfacial layers often cause unfavorable band alignment and interfacial states that lead to high charge-carrier recombination and eventually result in lower device performance. Herein, we demonstrate a simple and effective strategy to improve the performance of PSCs by constructing a conduction band offset (CBO) with a small spike, through the inductive effect induced by an organic small molecule. As a result, the modified devices show an enhancement in all photovoltaic performance characteristics with a power conversion efficiency (PCE) increase of 10.6% and retaining more than 94% of its initial PCE after 1800 h of exposure to N2. Importantly, we find that a moderate spike-like CBO at the interface between the perovskite film and hole transport layer facilitates rapid charge-carrier injection in devices and reduces charge recombination at the interface, thereby increasing the open-circuit voltage and fill factor. Furthermore, a large spike barrier at the interface increases device resistance, leading to a reduced fill factor. Our present work provides valuable information for understanding the influence of a spike-like CBO on charge-carrier dynamics to further improve the performance and stability of PSCs.

Photoelectrochemical study of Ti3+ self-doped Titania nanotubes arrays: A comparative study between chemical and electrochemical reduction

Water splitting through the photoelectrochemical process is a solid strategy to produce clean hydrogen for which TiO2 isconsideredthe most potential photoanode due to its unique properties. However, its wideband gap and high charge carrier recombination rate limit its solar-to-hydrogen conversion efficiency. Here in we report the fabrication of the Ti3+ self-doped TiO2 nanotube samples prepared through electrochemical and Chemical (NaBH4 treatment) reduction. Structural and morphological analysis carried through XRD and FESEM respectively confirmed the formation of TiO2 nanotube arrays. XPS spectra were used to affirm the presence of Ti3+ states in the reduced sample. The absorption edge observed in the 430–500 nm range validated the reduction of the band gap to the visible range in Ti3+ self-doped samples. Photoelectrochemical results of both the reduced samples evince their potential applicability as a photoanode for hydrogen generation through PEC water splitting. EIS and absorbance spectra reveal that larger charge density, faster electron-hole separation, and better visible light absorption may be thefactors that contribute to reducing TiO2′s superior photoelectrochemical performance. However, a comparative study shows better results for electrochemically reduced samples, suggesting it is an effective technique than chemical reduction.

Photocatalytic Carbon Dioxide Conversion by Structurally and Materially Modified Titanium Dioxide Nanostructures.

TiO2 has aroused considerable attentions as a promising photocatalytic material for decades due to its superior material properties in several fields such as energy and environment. However, the main dilemmas are its wide bandgap (3–3.2 eV), that restricts the light absorption in limited light wavelength region, and the comparatively high charge carrier recombination rate of TiO2, is a hurdle for efficient photocatalytic CO2 conversion. To tackle these problems, lots of researches have been implemented relating to structural and material modification to improve their material, optical, and electrical properties for more efficient photocatalytic CO2 conversion. Recent studies illustrate that crystal facet engineering could broaden the performance of the photocatalysts. As same as for nanostructures which have advantages such as improved light absorption, high surface area, directional charge transport, and efficient charge separation. Moreover, strategies such as doping, junction formation, and hydrogenation have resulted in a promoted photocatalytic performance. Such strategies can markedly change the electronic structure that lies behind the enhancement of the solar spectrum harnessing. In this review, we summarize the works that have been carried out for the enhancement of photocatalytic CO2 conversion by material and structural modification of TiO2 and TiO2-based photocatalytic system. Moreover, we discuss several strategies for synthesis and design of TiO2 photocatalysts for efficient CO2 conversion by nanostructure, structure design of photocatalysts, and material modification.

2D-Heterostructure assisted activation of MoS2 basal plane for enhanced photoelectrochemical hydrogen evolution reaction

As a potential catalyst of hydrogen evolution reaction (HER), molybdenum disulfide (MoS2) is known to have active sites at the edges, whereas its basal plane is inert. Thus activation of basal plane of MoS2 is essential to intensify the HER catalytic activity. Among various strategies, activation of MoS2 basal plane includes defects engineering via sulfur vacancies and hetero-atom doping. However, for optimal activation, requirements of defect concentration become impractically high, which increases defect-induced high charge carrier recombination loss in photoelectrochemical (PEC) HER. Herein, we report basal plane activation of MoS2 by heterostructuring with two-dimensional (2D) MoSe2 for enhanced photoelectrochemical HER. MoS2/MoSe2 heterostructure grown on silicon nanowire (SiNW) array shows 1.2 times higher photocurrent density and 1.36 times higher incident photon-to-current efficiency (IPCE) than pristine MoS2 grown on SiNW array along with 4.44 times higher H2 evolution rate compared to pristine SiNW photocathode. Density functional theory calculations of heterostructure reveal that charge transfer from the MoSe2 layer to the basal plane of MoS2 increases overall electron density resulting in its increased affinity towards proton reduction, which supports the experimental findings. These findings will boost the strategy for basal plane activation by 2D heterostructuring for efficient photoelectrochemical HER.