Development Of Photocatalysts Research Articles

Heterojunction Engineering of Multinary Metal Sulfide-Based Photocatalysts for Efficient Photocatalytic Hydrogen Evolution.

Photocatalytic hydrogen evolution (PHE) via water splitting using semiconductor photocatalysts is an effective path to solve the current energy crisis and environmental pollution. Heterojunction photocatalysts, containing two or more semiconductors, exhibit better PHE rates than those with only one semiconductor owing to the altered band alignment at the interface and stronger driving force for charge separation. Traditional binary metal sulfide (BMS)-based heterojunction photocatalysts, such as CdS, MoS2 , and PbS, demonstrate excellent PHE performance. However, the recently developed multinary metal sulfide (MMS)-based photocatalysts possess favorable chemical stability, tunable band structure, and flexible element compositions, and have considerable potential to realize higher PHE rates than those of BMSs. In this review article, the mechanism of PHE is first elucidated and then various single and heterojunction MMS-based photocatalysts and their charge transfer behaviors and PHE performances are systematically summarized. A perspective on potential future research directions in this field is concluded.

Single-atom Pt decorated g-C3N5 nanorods as highly efficient photocatalyst for H2 evolution and wastewater purification

Single-atom Pt decorated g-C3N5 nanorods (Pt SA/C3N5) were synthesized that exhibit highly efficient photocatalytic performance toward H2 evolution and wastewater purification. Implanting single Pt atoms into rod-like g-C3N5 through Pt–N coordination bonds could not only optimize its band structure, but also improve its specific surface area and promote the charge transfer. Therefore, the photocatalytic H2 evolution of Pt SA/C3N5 (444.2 μmol g−1 h−1) is about 4.4 times higher than that of C3N5 (102.0 μmol g−1 h−1), and its apparent quantum efficiency can reach 0.47 % at 420 nm. Furthermore, the degradation efficiency of Pt SA/C3N5 for Rhodamine B, Methylene blue and Malachite green is about 2.5, 1.6 and 1.5 times higher than that of C3N5, respectively. Moreover, Pt SA/C3N5 exhibits excellent stability on both the H2 evolution and wastewater purification. This research provides a neoteric way to build efficient photocatalysts that can be applied to energy and environment.

Development of a novel ternary FeWO4/CoP/Mn0.5Cd0.5S composite photocatalyst for photocatalytic hydrogen evolution in watersplitting

The construction of a non-homogeneous photocatalyst system with the advantages of both efficient photogenerated charge separation efficiency and abundant number of active sites remains a major challenge in the field of photocatalysis. A new ternary MnCdS-based photocatalyst combined with FeWO4 and CoP modifications was successfully prepared by chemical precipitation and thermal reduction methods. The ternary FeWO4/CoP/Mn0.5Cd0.5S photocatalyst exhibited a maximum hydrogen evolution activity of 30.45 mmol⋅g−1⋅h−1, which was 6.86 times higher than that of pureMn0.5Cd0.5S. The enhancement of the hydrogen production performance of the FeWO4/CoP/Mn0.5Cd0.5Sphotocatalyst was attributed to the p-n heterojunction constructed at the interface of FeWO4 and Mn0.5Cd0.5S, which strengthened the charge separation ability of the system. On the other hand, the decoration of CoP remarkably diminishes the hydrogen evolution potential of the system and supplies richer active sites for the catalytic reaction.

Boosting the water splitting and hydrogen production of S-scheme fabricated porous g-C3N4 modified with CuO

In response to the growing demand for sustainable hydrogen generation, particularly through solar energy conversion, this study focuses on the development of an S-scheme CuO/porous g-C3N4 (CuO/pCN) heterojunction nanocomposite for enhanced photocatalytic H2 evolution via water splitting under visible light. Coupling CuO with porous CN yields a remarkable H2 generation of 30 μmol/gh, about 5.29 times higher than CN (5.67 μmol/gh) and 2.78 times higher than pCN (10.78 μmol/gh). The superior performance of CuO/pCN is attributed to its highly porous structure with a large surface area (33.8 m2/g), which benefits the exposure of active sites, while a narrow band gap enhances photon absorption and utilization. Additionally, the formation of S-scheme heterojunction promotes more efficient separation of photoinduced charge carriers. CuO modification significantly enhances photocatalytic activity, contributing to efficient H2 production. A thorough investigation into crystal structure, surface morphology, and elemental composition elucidates characteristics responsible for heightened photochemical catalysis. The S-scheme heterojunction creation extends visible light absorption, achieving excellent photo-redox ability and mitigating photoinduced electron-hole recombination. In conclusion, this research presents a sustainable approach to efficient photocatalysts for hydrogen evolution, contributing to renewable energy production.

Machine Learning Accelerated Exploration of Ternary Organic Heterojunction Photocatalysts for Sacrificial Hydrogen Evolution.

Donor-acceptor heterojunctions in organic photocatalysts can provide enhanced exciton dissociation and charge separation, thereby improving the photocatalytic activity. However, the wide choice of possible donors and acceptors poses a challenge for the rational design of organic heterojunction photocatalysts, particularly for large ternary phase spaces. We accelerated the exploration of ternary organic heterojunction photocatalysts (TOHP) by using a combination of machine learning and high-throughput experimental screening. This involved 736 experiments in all, out of possible 4320 ternary combinations. The top ten most active TOHPs discovered using this strategy showed outstanding sacrificial hydrogen production rates of more than 500 mmol g-1 h-1, with the most active ternary material reaching a rate of 749.8 mmol g-1 h-1 under 1 sun illumination. These rates of photocatalytic hydrogen generation are among the highest reported for organic photocatalysts in the literature.

Synthesis of Graphene Based Graphitic Carbon Nitride Hybrid Nanocomposite Photocatalysts for Hydrogen Generation: A Mini Review

The discovery of visible active photocatalysts for H2 evolution via water splitting is the most awaited and critical goal of many researchers in recent years. Novel polymeric graphitic carbon nitride (GCN/g-CN) has emerged as a versatile material which has attracted the scientific community and industrialist because of its distinctiveness and outstanding electronic properties. g-CN is a metal free semiconductor as well as non-toxic, biodegradable polymeric material with low band gap energy which makes it a promising candidate as a photocatalyst and its efficiency as a catalyst can be modified by forming a hybrid nanocomposite with other semiconducting materials. Reduced graphene oxide, another metal free 2D material is a very good choice for this purpose. This review is an outlook for the synthesis processes and various properties of both g-CN and graphene. Further, it gives the approaches attempted towards the modifications required and done towards the development of a metal-free nano-hybrid material which is cost-effective, eco-friendly, and highly active visible light catalyst for the water- splitting process.

Oligo(phenylenevinylene)-Based Covalent Organic Frameworks with Kagome Lattice for Boosting Photocatalytic Hydrogen Evolution.

Covalent organic frameworks (COFs) have shown great advantages as photocatalysts for hydrogen evolution. However, the effect of linkage geometry and type of linkage on the extent of π-electron conjugation in the plane of the framework and photocatalytic properties of COFs remains a significant challenge. Herein, two Kagome (kgm) topologic oligo(phenylenevinylene)-based COFs are designed and synthesized for boosting photocatalytic hydrogen evolution via a "two in one" strategy. Under visible light irradiation, COF-954 with 5 wt% Pt as cocatalyst exhibits high hydrogen evolution rate (HER) of 137.23mmol g-1 h-1 , outperforming most reported COF-based photocatalysts. More importantly, even in natural seawater, COF-954 shows an average HER of 191.70mmol g-1 h-1 under ultraviolet-visible (UV-vis) light irradiation. Additionally, the water-drainage experiments indoors and outdoors demonstrate that 25 and 8mL hydrogen gas could be produced in 80 min under UV-vis light and natural sunlight, respectively, corresponding to a high HER of 167.41 and 53.57mmol h-1 g-1 . This work not only demonstrates an effective design strategy toward highly efficient COF-based photocatalysts, but also shows the great potential of using the COF-based photocatalysts for photocatalytic hydrogen evolution.

Schottky junction enhanced H2 evolution for graphitic carbon nitride-NiS composite photocatalysts

As one of the most promising photocatalysts for H2 evolution, graphitic carbon nitride (CN) has many appealing attributes. However, the activity of pristine CN remains unsatisfactory due to severe charge carrier recombination and lack of active sites. In this study, we report a two-step approach for the synthesis of CN nanotubes (TCN) loaded with NiS nanoparticles. The resulting composite photocatalysts gave a H2 evolution rate of 752.9 μmol g−1 h−1, which is 42.3 times higher compared to the pristine CN photocatalyst. Experimental and simulation results showed that the Schottky junction which was formed between TCN and NiS was key to achieving high activity. This is because the formation of Schottky junction prevented the backflow of electrons from NiS to TCN, which improved charge separation efficiency. More importantly, it also led to the accumulation of electrons on NiS, which significantly weakened the SH bond, such that the intermediate hydrogen species desorbed more easily from NiS surface to promote H2 evolution activity.

Synergistic effect of surface oxygen vacancies and hydroxyl groups on Cu-doped TiO2 photocatalyst for hydrogen evolution

The intricate nature of the titanium dioxide (TiO2) photocatalytic system, influenced by Cu doping, often yields conflicting outcomes. This study addresses this complexity by examining the impact of Cu ion doping in nanostructured TiO2 to augment its photocatalytic efficacy in hydrogen generation from ethanol-water mixtures. The improved performance is primarily attributed to the generation of oxygen vacancies (Ovac) within the TiO2 lattice. By adjusting the thermal processing parameters, the chemical state of Cu is modulated to optimize photocatalytic performance. Solid-state nuclear magnetic resonance (SSNMR) and density functional theory (DFT) calculations confirm that the presence of Ovac and hydroxyl groups (OH−) surface species not only facilitates local spatial charge separation but also enhances light absorption, thereby improving photocatalytic hydrogen evolution reaction (HER) rate up to 20.2 mmol h−1 g−1 under UV light. Furthermore, a proposed mechanism involves the participation of Ovac and OH− species, supported by Mott-Schottky (M − S) plots and ultraviolet photoelectron spectroscopy (UPS), revealing that Cu–TiO2 exhibits a lower flat band potential (Efb) and smaller work function compared to TiO2. This research underscores the pivotal role of Cu ions and Ovac:OH− in advancing the photocatalytic activity of TiO2-based crystals, imparting noteworthy implications for sustainable hydrogen generation.

Structural, mechanical, electronic and optical properties of Si decorated zinc oxide nanotube photocatalyst for hydrogen evolution via overall water splitting: A DFT study

This work investigated an Si-doped single-walled zinc oxide nanotube (SWZnONT) as photocatalyst for hydrogen energy production. Photocatalytic properties of the Si-doped SWZnONT were determined based on analysis of structural, electronic and optical absorption spectra using density functional theory. The obtained data for structural and mechanical properties of the systems revealed that Si-doped SWZnONT was stable under 2.7 % and 5.5 % of Si concentrations. Furthermore, the studied SWZnONT doped with 2.7 % Si demonstrated an indirect band gap of 2.6 eV which is desirable to be an ideal photocatalyst. Results from optical spectra analysis revealed that Photo-generated holes on the Si-doped SWZnONT surface promote water splitting.

A novel MoS2-modified hybrid nanodiamond/g-C3N4 photocatalyst for photocatalytic hydrogen evolution

A novel double-heterojunction MoS2/hybrid nanodiamond/g-C3N4 (MoS2/HND/g-C3N4) heterojunction photocatalyst was synthesized by hydrothermal method. The photocatalytic performance of MoS2/HND/g-C3N4 toward H2 evolution was superior to that of the binary one. In particular, under visible-light irradiation, the MoS2/HND/g-C3N4 nanocomposite photocatalyst with 4 wt% of MoS2 and 3 wt% of HND exhibited the highest photocatalytic hydrogen evolution activity and its corresponding H2 evolution rate is 227 μmol g-1h−1, which was about 34 times higher than that of g-C3N4/MoS2-3 %. The origin of the high efficiency can be ascribed to three aspects: (i) graphene shell of HND with high carrier mobility can shorten the charge migration time while the diamond core with light scatter effect can enhance the light absorption efficiency; (ii) the heterostructure formed at the interface of different components can accelerate the charge transfer and separation; (iii) MoS2 quantum dots as cocatalyst can provide active sites, which were needed in the photocatalytic action.

Enhanced Z-scheme water splitting at atmospheric pressure with suppression of reverse reactions using Zr-doped BaTaO2N as hydrogen evolution photocatalyst

The present work demonstrates a Z-scheme overall water splitting (ZOWS) system for the photocatalytic production of H2 capable of operating under Ar at near-atmospheric pressure using a narrow-bandgap Zr-doped BaTaO2N photocatalyst. Reverse reactions are suppressed in this system as a consequence of a surface modification of the Pt-loaded, Zr-doped BaTaO2N (Pt/BaTaO2N:Zr) photocatalyst with Cr2O3. The introduction of a Cr2O3 shell was found to effectively inhibit the reduction of [Fe(CN)6]3- that otherwise competes with the H2 evolution reaction, resulting in an improved apparent quantum yield of 1.1 % at 420 nm. By combining this H2 evolution photocatalyst with an O2 evolution photocatalyst based on BiVO4, ZOWS was achieved at near-atmospheric pressure with a solar-to-hydrogen energy conversion efficiency of 0.08 %. This work demonstrates the importance of suppressing reverse reactions during ZOWS at atmospheric pressure and provides valuable guidance for the design and construction of practical green H2 production systems.

Structural, mechanical, electronic and optical properties of N-decorated single-walled silicon carbide nanotube photocatalyst for hydrogen evolution via water splitting: a DFT study

ABSTRACT This work investigates the fundamental photocatalytic properties of nitrogen-doped single-walled silicon carbide nanotubes (N-doped SWSiCNTs) for hydrogen evolution for the first time. Investigations of the structural, mechanical, electronic, and optical properties of the studied systems were carried out using popular density functional theory implemented in quantum ESPRESSO and Yambo codes. Analysis of the structural properties revealed high mechanical stability with the 3.6% and 7.4% N-doped SWSiCNT. The calculated band gap of the N-doped SWSiCNT with 3.6% demonstrated a value of 2.56 eV which is within the photocatalytic range of 2.3 eV−2.8 eV. The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) potentials of the 3.6% N-doped SWSiCNT also showed good agreement with previous theoretical data. The studied material showed the best photocatalytic performance in both parallel and perpendicular directions by absorbing photons in the visible region. Therefore, the observed structural, mechanical, electronic and optical behaviors demonstrated by the 3.6% N-doped SWSiCNT exposed it as a better photocatalyst for hydrogen production under visible light.

DFT Studies of the Photocatalytic Properties of MoS2-Doped Boron Nitride Nanotubes for Hydrogen Production.

This study investigated the photocatalytic properties of MoS2-doped boron nitride nanotubes (BNNTs) for overall water splitting using popular density functional theory (DFT). Calculations of the structural, mechanical, electronic, and optical properties of the investigated systems were performed using both the generalized gradient approximation and the GW quasi-particle correction methods. In our calculations, it was observed that only (10, 10) and (12, 12) single-walled BNNTs (SWBNNTs) turned out to be stable toward MoS2 doping. Electronic property calculations revealed metallic behavior of (10, 10)-MoS2-doped SWBNNTs, while the band gap of (12, 12) SWBNNT was narrowed to 2.5 eV after MoS2 doping, which is within the obtained band gaps for other photocatalysts. Hence, MoS2 influences the conduction band of pure BNNT and improves its photocatalytic properties. The water-splitting photocatalytic behavior is found in (12, 12) MoS2-doped SWBNNT, which showed higher water oxidation (OH-/O2) and reduction (H+/H2) potentials. In addition, optical spectral calculations showed that MoS2-doped SWBNNT had an optical absorption edge of 2.6 eV and a higher absorption in the visible region. All of the studied properties confirmed MoS2-doped SWBNNT as a better candidate for next-generation photocatalysts for hydrogen evolution through the overall water-splitting process.

Preparation strategy of bimetallic MOF hollow photocatalysts for hydrogen evolution

Hollow structure materials have been proved to be excellent photocatalysts due to their advantages in the separation of electron-hole pairs. However, the synthesis of such materials is complex, time-consuming, and poor versatility. In this study, Cu-DHTP/ZIF-67 (DHTP = 2,5-dihydroxyterephthalic acid) hollow materials containing both Co and Cu were designed and synthesized by a simple one-step etching and ligand exchange strategy. It is worth noting that the bimetallic hollow catalyst can be synthesized in the presence of both Cu(Ⅱ) and DHTP within 5 min at room temperature. The synthesized hollow bimetallic catalyst has improved photoresponse performance and electron-hole pair separation ability, which results in the best catalytic performance compared with DHTP/ZIF-67, Cu/ZIF-67, and ZIF-67 when used in the photocatalytic water splitting reaction. The hydrogen evolution yield of Cu-DHTP/ZIF-67 can reach 39.7 mmol g−1, which is 6 times than that of pure ZIF-67. This study demonstrates the promising potential of Cu-DHTP/ZIF-67 photocatalyst in the field of photocatalytic water reduction and hydrogen evolution, and provides a new idea for designing and preparing more hollow structure bimetallic photocatalysts with excellent performance.

Electronic coupling between metallic Ni and VN nanoparticles enables g-C3N4 nanosheet as an efficient photocatalyst for hydrogen evolution

Developing highly efficient hydrogen evolution cocatalysts is of great significance for semiconductor photocatalysts toward the large-scale conversion of solar light energy into clean hydrogen fuel. Herein, a novel Ni/VN hetero-nanosheets is reported for the first time, as precious metal-free co-catalyst for g-C3N4, and the electronic coupling between Ni and VN greatly promotes the photocatalytic hydrogen production activity of g-C3N4 nanosheet (CNNS) under visible-light irradiation. As expected, CNNS with 3 wt% Ni/VN (CNNS/Ni/VN) exhibits excellent photocatalytic activity with hydrogen production rates are as high as 417.1 μmol h−1g−1. In addition, CNNS/Ni/VN has excellent cyclic hydrogen production stability for 24 h. This excellent performance is attributed to the strong electron coupling between Ni and VN. Therefore, the Ni/VN cocatalysts will open a newfangled way for powerful solar-fuel production.

Synthesis of mesoporous p-CuAl2O4/n-YVO4 heterojunction nanocomposites and their utilization as effective photocatalysts for hydrogen evolution

The photocatalytic H2 evolution processes have received great attention from the scientific society using semiconductor photocatalysts, and the main bottleneck for the newly synthesized photocatalyst is the swift recombination rate of photoinduced holes and electrons. In this contribution, heterojunction p-CuAl2O4/n-YVO4 photocatalyst was synthesized through the facile sol–gel process utilizing the block copolymer templating. The photocatalytic ability and stability of the p-CuAl2O4/n-YVO4 heterojunction photocatalysts have been examined by H2 evolution in glycerol solution as a hole scavenger under visible illumination. TEM and XRD analyses indicated the formation of YVO4 (5–10 nm) with a tetragonal structure and their uniform interaction with spinel-type CuAl2O4 (5 nm). The CuAl2O4/YVO4 nanocomposites were verified for the first time to be competitive photocatalysts for H2 evolution compared with bare YVO4 NPs. At optimum conditions, the 15 % CuAl2O4/YVO4 nanocomposite revealed an enhanced H2 evolution rate (2994.6 µmolg-1h−1), about 72.5-fold that of bare YVO4 NPs (41.3 µmolg-1h−1). The heterojunction interface of p-CuAl2O4/n-YVO4 NPs was constructed according to their band structures to build S-scheme mechanism. The photoelectrochemical and PL measurements of the CuAl2O4/YVO4 photocatalysts are systematically examined to confirm our photocatalytic H2 evolution studies. It revealed that introducing CuAl2O4 on YVO4 effectively inhibited the recombination of photocarriers, thus promoting the H2 evolution rate. The work provides advantages for plausible designing p-n heterostructures and exhibits new insight to promote photocatalytic performance for potential applications.

Construction of rGO/BP/COF high-low heterojunction for efficient photocatalytic hydrogen evolution

The covalent organic frameworks (COFs) have emerged as potential photocatalysts for solar-driven hydrogen evolution, but the disadvantage that photogenerated electrons and holes are prone to recombination limits their applications. Here, a rGO/BP/TpPa-1 high-low heterojunction with electron acceptors was prepared by integrating reduced graphene oxide (rGO) and black phosphorus (BP) into COF TpPa-1 to reduce the recombination rate of photoinduced charge carriers. The photocatalytic hydrogen evolution rate reached 18.09 mmol h−1 g−1, about 3.3 times higher than pure TpPa-1. Here, a two-step photogenerated electron transfer mechanism is proposed. Firstly, a high-low heterojunction is formed between TpPa-1 and BP through an internal electric field from BP to TpPa-1, facilitating photogenerated electrons transfer from TpPa-1 to BP, then rGO attached to the BP surface acts as an electron acceptor, further collecting photogenerated electrons for reaction. This work provides a novel strategy for synthetizing efficient COF-based photocatalysts.

Enrichment and activation of cyano in cobalt hexacyanoferrate for specific recovery of ultra-low concentrations of platinum

Adsorption recovery of ultra-low concentrations (1 ppm) of platinum (Pt) was challenging due to the inferior sensitivity response and poor specific affinity between sorbents and target ions. Herein, enrichment and activation of the cyano group (CN) on cobalt hexacyanoferrate (CoHCF) were achieved by crystal facets engineering to capture Pt(Ⅱ) efficiently and specifically. The Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and density-functional theory (DFT) calculations results revealed that the activity and density of CN on the (220) facets were higher than that on the (200) facet. The Pt(Ⅱ) adsorption efficiency on the CN-enriched and -activated CoHCF (CoHCF(220)) reached 92.5%, which was 1.56 times higher than that on the original CoHCF (59.2%). The specific adsorption of Pt(Ⅱ) was driven by the coordination interaction between Fe-CN– and Pt, leading to the Pt(Ⅱ)-Pd(Ⅱ) separation efficiency attained 98.95% within 20 min. In addition, CoHCF(220) equipped with Pt(Ⅱ) could be further chemically reduced as a photocatalyst for hydrogen evolution. This study suggested an attractive strategy for the practical recovery of Pt(Ⅱ) and comprehensive utilization of ultra-low concentration Pt-containing wastewater.

Graphdiyne (g-CnH2n-2) boosting electron transfer over rational design and construction of CuI/Ni-MOF photocatalyst for efficient hydrogen evolution

A CuI-graphdiyne/Ni-MOF ternary system was successfully constructed. Intially, CuI-graphdiyne was obtained by growth of GDY on the surface of CuI. Subequently, the CuI-graphdiyne was immobilized onto the surface of Ni-MOF using a simple physical stirring method. This, immobilization approach effectively reducing the accumulation of CuI-graphdiyne and increased the number of active sites for hydrogen evolution. Furthermore, a combination of various characterization techniques and energy band structures analysis was employed to propose the photocatalytic reaction mechanism between CuI and Ni-MOF. The proposed mechanism involves a Z-scheme heterojunction and suggests that the combination of CuI and Ni-MOF enhances the overall redox ability of the composite catalyst. By comparing CuI/Ni-MOF with CuI-graphdiyne/Ni-MOF, it was observed that the presence of graphdiyne as an electron-rich layer on CuI enhances the photocatalytic performance of CuI. Additionally, it facilitates electron transport between CuI and Ni-MOF, thereby improving the efficiency of photogenerated electron-hole complex separation. This experimental study provides valuable insight into the utilization of graphdiyne for enhancing transport in heterojunction.