Surface-Alkalinization-Induced Enhancement of Photocatalytic H2 Evolution over SrTiO3-Based Photocatalysts

Copper Single-Atom Catalysts-A Rising Star for Energy Conversion and Environmental Purification: Synthesis, Modification, and Advanced Applications

Future renewable energy supply and green, sustainable environmental development rely on various types of catalytic reactions. Copper single-atom catalysts (Cu SACs) are attractive due to their distinctive electronic structure (3d orbitals are not filled with valence electrons), high atomic utilization, and excellent catalytic performance and selectivity. Despite numerous optimization studies are conducted on Cu SACs in terms of energy conversion and environmental purification, the coupling among Cu atoms-support interactions, active sites, and catalytic performance remains unclear, and a systematic review of Cu SACs is lacking. To this end, this work summarizes the recent advances of Cu SACs. The synthesis strategies of Cu SACs, metal-support interactions between Cu single atoms and different supports, modification methods including modification for carriers, coordination environment regulating, site distance effect utilizing, and dual metal active center catalysts constructing, as well as their applications in energy conversion and environmental purification are emphatically introduced. Finally, the opportunities and challenges for the future Cu SACs development are discussed. This review aims to provide insight into Cu SACs and a reference for their optimal design and wide application.

Dual S-Scheme Heterojunction CdS/TiO2/g-C3N4 Photocatalyst for Hydrogen Production and Dye Degradation Applications

This study investigated a ternary CdS/TiO2/g-C3N4 heterojunction for degrading synthetic dyes and hydrogen production from aqueous media through visible light-initiated photocatalytic reactions. CdS, TiO2, and g-C3N4 were combined in different mass ratios through a simple hydrothermal method to create CdS/TiO2/g-C3N4 composite photocatalysts. The prepared heterojunction catalysts were investigated by using FTIR, XRD, EDX, SEM, and UV-visible spectroscopy analysis for their crystal structures, functional groups, elemental composition, microtopography, and optical properties. The rhodamine B dye was then degraded by using fully characterized photocatalysts. The maximum dye degradation efficiency of 99.4% was noted in these experiments. The evolution rate of hydrogen from the aqueous solution with the CdS/TiO2/g-C3N4 photocatalyst remained 2910 μmol·h-1·g-1, which is considerably higher than those of g-C3N4, CdS, CdS/g-C3N4, and g-C3N4/TiO2-catalyzed reactions. This study also proposes a photocatalytic activity mechanism for the tested ternary CdS/TiO2/g-C3N4 heterojunctions.

Penta-MP5 (M = B, Al, Ga, In) monolayers as high-performance photocatalysts for overall water splitting

Two-dimensional (2D) phosphorus-rich phosphides generally preserve the excellent electronic properties of phosphorene, making them promising photocatalysts for water splitting. Despite tremendous efforts in the search for potential photocatalysts in 2D phosphides, few known 2D phosphides fully meet the requirements for photocatalytic water splitting. Herein, we systemically investigate a set of penta-MP5 (M = B, Al, Ga, and In) monolayers by first-principles calculations and identify them as potential photocatalysts for water splitting. These penta-MP5 monolayers are found to feature favorable bandgaps of about 2.70 eV with appropriate band edge positions, a high carrier mobility of 1 × 104 cm-2 V-1 s-1, an excellent optical absorption coefficient (OAC) of 1 × 105 cm-1, and a good solar-to-hydrogen (STH) efficiency of 8%. Meanwhile, free energy calculations indicate that these penta-MP5 monolayers present both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) photocatalytic activities under light conditions. All these excellent properties demonstrate that penta-MP5 monolayers are suitable candidates as photocatalysts for promising applications in overall water splitting.

Pd/Ni bimetallic modification of SrTiO3for enhancement of photocatalytic water splitting

This paper investigates the impact of Pd/Ni modification on the photocatalytic hydrogen production performance of SrTiO3(STO). STO catalysts were synthesized using a hydrothermal method, and Pd/Ni modification was applied on the surface of STO through chemical deposition. Experimental results demonstrate that the hydrogen evolution rate of Pd/Ni-modified STO (Pd/Ni-STO) reaches 2232.14μmol g-1h-1. X-ray absorption fine structure spectroscopy analysis reveals substitutional doping of Ni with Ti and coordination of Pd with surface O. X-ray photoelectron spectroscopy analysis indicates the introduction of oxygen vacancies due to Pd/Ni doping. Density functional theory calculations suggest that Ni doping activates neighboring Ti atoms, leading to the formation of bimetallic catalytic sites composed of oxygen vacancies and Ti atoms, greatly enhancing the photocatalytic hydrogen evolution performance. This study not only provides an effective catalyst for photocatalytic applications but also offers insights into the underlying mechanism, which may stimulate the development of metal-doped catalytic materials and have implications for a range of other applications.

Dynamic active-site induced by host-guest interactions boost the Fenton-like reaction for organic wastewater treatment

In heterogeneous catalysis, uncovering the dynamic evolution of active sites in the working conditions is crucial to realizing increased activity and enhanced stability of catalyst in Fenton-like activation. Herein, we capture the dynamic changes in the unit cell of Co/La-SrTiO₃ catalyst during the exemplary peroxymonosulfate activation process using X-ray absorption spectroscopy and in situ Raman spectroscopy, revealing the substrate tuned its structural evolution, which is the reversible stretching vibration of O-Sr-O and Co/Ti-O bonds in different orientations. This process effectively promotes the generation of key SO₅* intermediates, which is beneficial to the formation of ¹O₂ and SO₄^•- from persulfate on the Co active site. Density functional theory and X-ray absorption spectroscopy show that the optimized structural distortion enhanced the metal-oxygen bond strength by tuning the e_g orbitals and increased the number of transferred electrons to peroxymonosulfate by about 3-fold, achieving excellent efficiency and stability in removing organic pollutants.

The Role of the Ferroelectric Polarization in the Enhancement of the Photocatalytic Response of Copper-Doped Graphene Oxide-TiO2 Nanotubes through the Addition of Strontium

To evaluate the potential role of in situ formed Sr-Ti-O species as a ferroelectric component able to enhance the photocatalytic properties of an adjacent TiO₂ semiconductor, Cu-doped/graphene oxide (GO)/TiO₂ nanotubes (TiNTs) composites (with 0.5 wt % Cu and 1.0 wt % GO) have been synthesized while progressive amounts of strontium (up to 1.0 wt %) were incorporated at the surface of the composite through incipient wetness impregnation followed by post-thermal treatment at 400 °C. The different resulting photocatalytic systems were then first deeply characterized by means of N₂ adsorption-desorption measurements, X-ray diffraction (XRD), UV-vis diffuse reflectance (UV-vis DR), Raman and photoluminescence (PL) spectroscopies, and scanning electron microscopy (SEM) (with energy-dispersive X-ray (EDX) spectroscopy and Z-mapping). In a second step, optimization of the kinetic response of the Sr-containing composites was performed for the formic acid photodegradation under UV irradiation. The Sr-containing Cu/GO/TiNT composites were then fully characterized by electrochemical impedance spectroscopy (EIS) for their dielectric properties showing clearly the implication of polarization induced by the Sr addition onto the stabilization of photogenerated charges. Finally, a perfect correlation between the photocatalytic kinetic evaluation and dielectric properties undoubtedly emphasizes the role of ferroelectric polarization as a very valuable approach to enhance the photocatalytic properties in an adjacent semiconductor.

Recent trends in Bi-based nanomaterials: challenges, fabrication, enhancement techniques, and environmental applications

One of the most enticing approaches to environmental restoration and energy conversion is photocatalysis powered by solar light. Traditional photocatalysts have limited practical uses due to inadequate light absorption, charge separation, and unknown reaction mechanisms. Discovering new visible-light photocatalysts and investigating their modification is crucial in photocatalysis. Bi-based photocatalytic nanomaterials have gotten much interest as they exhibit distinctive geometric shapes, flexible electronic structures, and good photocatalytic performance under visible light. They can be employed as stand-alone photocatalysts for pollution control and energy production, but they do not have optimum efficacy. As a result, their photocatalytic effectiveness has been significantly improved in the recent decades. Numerous newly created concepts and methodologies have brought significant progress in defining the fundamental features of photocatalysts, upgrading the photocatalytic ability, and understanding essential reactions of the photocatalytic process. This paper provides insights into the characteristics of Bi-based photocatalysts, making them a promising future nanomaterial for environmental remediation. The current review discusses the fabrication techniques and enhancement in Bi-based semiconductor photocatalysts. Various environmental applications, such as H₂ generation and elimination of water pollutants, are also discussed in terms of semiconductor photocatalysis. Future developments will be guided by the uses, issues, and possibilities of Bi-based photocatalysts.

Construction of SrTiO3–LaCrO3 Solid Solutions with Consecutive Band Structures for Photocatalytic H2 Evolution under Visible Light Irradiation

SrTiO3–LaCrO3 continuous solid solutions with LaCrO3 content ranging from 0.00 to 1.00 were prepared via a polymerized complex method. The light absorption ability of SrTiO3 was improved by the consecutive tuning of the bandgap upon the introduction of LaCrO3 (up to 570 nm). The solid solutions exhibited significantly enhanced photocatalytic activities for H2 evolution under visible light irradiation, with an optimized H2 evolution rate of 1368 μmol h−1 g−1 obtained when LaCrO3 content was 0.10 (with 1 wt% Pt as cocatalyst), corresponding to an apparent quantum yield of 3.68% at 400 nm. Supported by comprehensive characterization, the improved photocatalytic performance was attributed to the simultaneously adjusted conduction band and valance band originating from the hybridization of Cr 3d, Ti 3d and O 2p orbitals, as well as the accelerated separation and migration of photogenerated charge carriers derived from the distortion of TiO6 octahedra.

Photothermal Synergistic Effect of Pt1/CuO-CeO2 Single-Atom Catalysts Significantly Improving Toluene Removal

Photothermal synergistic catalytic oxidation of toluene over single-atom Pt catalysts was investigated. Compared with the conventional thermocatalytic oxidation in the dark, toluene conversion and CO₂ yield over 0.39Pt₁/CuO-CeO₂ under simulated solar irradiation (λ = 320-2500 nm, optical power density = 200 mW cm^-2) at 180 °C could be increased about 48%. An amount of CuO was added to CeO₂ to disperse single-atom Pt with a maximal Pt loading of 0.83 wt %. The synergistic effect between photo- and thermocatalysis is very important for the development of new pollutant treatment technology with high efficiency and low energy consumption. Both light and heat played an important role in the present photothermal synergistic catalytic oxidation. 0.39Pt₁/CuO-CeO₂ showed good redox performance and excellent optical properties and utilized the full-spectrum solar energy. Light illumination induced the generation of reactive oxygen species (^•OH and ^•O₂^-), which accelerated the transformation of intermediates, promoted the release of active sites on the catalyst surface, and improved the oxidation reaction.

Insight into the effect of OH modification on the piezo-photocatalytic hydrogen production activity of SrTiO3

Surface modification by hydrophilic functional group have a tremendous influence on the catalytic activity of photocatalyst, however, there are few reports on improving piezoelectric catalytic performance through surface functionalization. Herein, OH-modified SrTiO₃ was successfully obtained via a novel low-temperature solid-state precursor method and employed as a catalyst for photocatalytic, piezocatalytic and piezo-photocatalytic hydrogen production. Thanks to the super hydrophilic that is facilitating the contact of catalyst and water molecular and the more oxygen vacancies that can promote electron-hole separation, the photocatalytic, piezocatalytic and piezo-photocatalytic hydrogen generation of OH-modified SrTiO₃ (OH-STO) is about two times higher than pristine SrTiO₃ (STO). It is worth mentioning that the optimal piezo-photocatalytic hydrogen evolution rate of OH-STO (701.2 µmol h^-1 g^-1) is 5.3 times higher than the photocatalytic hydrogen evolution process of STO. This study presents a low-energy approach to the rational design of functional group modification nanomaterials that possess excellent piezo-photocatalytic performance.

The Fabrication of Pd Single Atoms/Clusters on COF Layers as Co-catalysts for Photocatalytic H2 Evolution

The particle size of co-catalysts significantly affects the activity of semiconductors in photocatalysis. Herein, we report that the photocatalytic H₂ evolution (PHE) activity of a visible light responsive covalent organic framework (COF) layer supported on SiO₂ nanoparticles was greatly promoted from 47.7 to 85.5 μmol/h by decreasing the particle size of the Pd co-catalyst from 3.3 nm to single atoms/clusters. A PHE rate of 156 mmol g_COF^-1 h^-1 and apparent quantum efficiency up to 7.3% were achieved with the Pd SAs/Cs co-catalyst. The relationship between the activity of Pd in H₂ dissociation, proton reduction, and PHE rate suggests that the promotion effect of Pd SAs/Cs is mainly attributed to their enhancement in charge separation of COF layers rather than proton reduction. Furthermore, a photoactive film was fabricated and steady production of H₂ was achieved under visible light irradiation and static conditions. The optimization of the particle size of co-catalysts provides an efficient method for enhancing the photocatalytic activity of semiconductors.

General Strategy for ATiO3 (A = Ca, Sr, or Ba) Submicrospheres with Large Surface Area and its Photocatalytic Applications

Porous CaTiO3 solid submicrospheres, SrTiO3 and BaTiO3 hollow submicrospheres, which had larger surface area (40.21 to 228.18 m2·g-1) and uniform particle size, were synthesized by self-template assisted hydrothermal method with...

Mesoporous perovskite titanates via hydrothermal conversion

We demonstrate the successful hydrothermal conversion of mesoporous TiO₂ to mesoporous perovskite SrTiO₃. This method allows for control of pore size distribution and can be readily applied for the preparation of other mesoporous titanates such as BaTiO₃ and Li₂TiO₃. Such high-surface perovskites have potential in high-temperature applications due to their thermal stability.

Developing sustainable, high-performance perovskites in photocatalysis: design strategies and applications

Solar energy is attractive because it is free, renewable, abundant and sustainable. Photocatalysis is one of the feasible routes to utilize solar energy for the degradation of pollutants and the production of fuel. Perovskites and their derivatives have received substantial attention in both photocatalytic wastewater treatment and energy production because of their highly tailorable structural and physicochemical properties. This review illustrates the basic principles of photocatalytic reactions and the application of these principles to the design of robust and sustainable perovskite photocatalysts. It details the structures of the perovskites and the physics and chemistry behind photocatalytic reactions and describes the advantages and limitations of popular strategies for the design of photoactive perovskites. This is followed by examples of how these strategies are applied to enhance the photocatalytic efficiency of oxide, halide and oxyhalide perovskites, with a focus on materials with potential for practical application, that is, not containing scarce or toxic elements. It is expected that this overview of the development of photocatalysts and deeper understanding of photocatalytic principles will accelerate the exploitation of efficient perovskite photocatalysts and bring about effective solutions to the energy and environmental crisis.

Synergetic modulation of surface alkali and oxygen vacancy over SrTiO3for the CO2photodissociation

Photochemical conversion of CO₂into solar fuels is one of the promising strategies to reducing the CO₂emission and developing a sustainable carbon economy. For the more efficient utilization of solar spectrum, several approaches were adopted to pursue the visible-light-driven SrTiO₃. Herein, oxygen vacancy was introduced over the commercial SrTiO₃(SrTiO_3-x) via the NaBH₄thermal treatment, to extend the light absorption and promote the CO₂adsorption over SrTiO₃. Due to the mid-gap states resulted from the oxygen deficiency, combined with the intrinsic energy level of SrTiO₃, the SrTiO_3-xcatalyst exhibited excellent CO productivity (4.1 μmolˑg^-1ˑh^-1) and stability from the CO₂photodissociation under the visible-light irradiation (λ > 400 nm). Then, surface alkalization over SrTiO_3-x(OH-SrTiO_3-x) was carried out to further enhance the CO₂adsorption/activation over the surface base sites and provide the OH ions as hole acceptor, the surface alkali OH connected with Sr site of SrTiO₃could also weaken the Sr-O bonding thus facilitate the regeneration of surface oxygen vacancy under the light illumination, thus resulting in 1.5 times higher CO productivity additionally. This study demonstrates that the synergetic modulation of alkali OH and oxygen vacancy over SrTiO₃could largely promote the CO₂photodissociation activity.

Photoinduced electronic and ionic effects in strontium titanate

The interaction of light with solids has been of ever-growing interest for centuries, even more so since the quest for sustainable utilization and storage of solar energy became a major task for industry and research. With SrTiO₃ being a model material for an extensive exploration of the defect chemistry of mixed conducting perovskite oxides, it has also been a vanguard in advancing the understanding of the interaction between light and the electronic and ionic structure of solids. In the course of these efforts, many phenomena occurring during or subsequent to the illumination of SrTiO₃ have been investigated. Here, we give an overview of the numerous photoinduced effects in SrTiO₃ and their inherent connection to electronic structure and defect chemistry. In more detail, advances in the fields of photoconductivity, photoluminescence, photovoltages, photochromism and photocatalysis are summarized and their underlying elemental processes are discussed. In light of recent research, this review also emphasizes the fundamental differences between illuminating SrTiO₃ either at low temperatures (<RT) or at high temperatures (>200 °C), where in addition to electronic processes, also photoionic interactions become relevant. A survey of the multitude of different processes shows that a profound and comprehensive understanding of the defect chemistry and its alteration under illumination is both vital to optimizing devices and to pushing the boundaries of research and advancing the fundamental understanding of solids.

A Multi-Layer Device for Light-Triggered Hydrogen Production from Alkaline Methanol

It usually requires high temperature and high pressure to reform methanol with water to hydrogen with high turnover frequency (TOF). Here we show that hydrogen can be produced from alkaline methanol on a light‐triggered multi‐layer system with a very high hydrogen evolution rate up to ca. 1 μmol s⁻¹ under the illumination of a standard Pt‐decorated carbon nitride. The system can achieve a remarkable TOF up to 1.8×10⁶ moles of hydrogen per mole of Pt per hour under mild conditions. The total turnover number (TTN) of 470 000 measured over 38 hours is among the highest reported. The system does not lead to any CO_x emissions, hence it could feed clean hydrogen to fuel cells. In contrast to a slurry system, the proposed multi‐layer system avoids particle aggregation and effectively uses light and Pt active sites. The performance is also attributed to the light‐triggered reforming of alkaline methanol. This notable performance is a promising step toward practical light‐driven hydrogen generation.

Synthesis of a Visible-Light-Responsive Perovskite SmTiO2 N Bifunctional Photocatalyst via an Evaporation-Assisted Layered-Precursor Strategy

Development of visible-light-responsive oxynitride photocatalysts has been highly inspired for promising solar-to-chemical conversion, but the number of Ti-based oxynitrides is scarce because of the relatively low thermal stability of Ti⁴⁺ ions under ammonia flow. Here, the feasible synthesis of a novel perovskite SmTiO₂ N from the layered NaSmTiO₄ precursor is demonstrated to exhibit wide visible-light response with a bandgap of ≈2.1 eV and to show effective water reduction and oxidation functionalities under visible-light irradiation. The successful preparation mainly results from the synergistic effect of the layered structure of NaSmTiO₄ and the evaporation spillover of Na⁺ ions, both of which are favorable for ammonia diffusion to accelerate the substitution of nitrogen to oxygen atoms and to shorten the nitridation time. The thermodynamic and kinetic feasibility of SmTiO₂ N for water splitting are investigated in detail, and its optimal apparent quantum efficiency (AQE) of water oxidation reaches 16.7% at 420 ± 10 nm, higher by far than that of most previous visible-light-responsive photocatalysts. Interestingly, a series of oxynitrides RTiO₂ N (R = La, Pr, Nd) are similarly synthesized by the alkali-metal evaporation-assisted layered-precursor strategy, demonstrating its generality to prepare visible-light-responsive (oxy)nitride photocatalysts containing reducible metals for solar energy conversion.

Manipulating the Structure and Characterization of Sr1−xLaxTiO3 Nanocubes toward the Photodegradation of 2-Naphthol under Artificial Solar Light

Effective La-doped SrTiO3 (Sr1−xLaxTiO3, x = 0–0.1 mol.% La-doped) nanocubes were successfully synthesized by a hydrothermal method. The influence of different La dopant concentrations on the physicochemical properties of the host structure of SrTiO3 was fully characterized. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) revealed that the Sr2+ in the crystal lattice of SrTiO3 was substituted by La3+. As a result, the absorption region of the Sr1−xLaxTiO3 could be extended to visible light. Scanning electron microscopy (SEM) images confirmed that their morphologies are associated with an increased surface area and an increased La-doping concentration. The decrease in the photoluminescence (PL) intensity of the dopant samples showed more defect levels created by the dopant La+3 cations in the SrTiO3 structure. The photocatalytic activities of Sr1−xLaxTiO3 were evaluated with regard to the degradation of 2-naphthol at typical conditions under artificial solar light. Among the candidates, Sr0.95La0.05TiO3 exhibited the highest photocatalytic performance for the degradation of 2-naphthol, which reached 92% degradation efficiency, corresponding to a 0.0196 min−1 degradation rate constant, within 180 minutes of irradiation. Manipulating the structure of Sr1−xLaxTiO3 nanocubes could produce a more effective and stable degradation efficiency than their parent compound, SrTiO3. The parameters remarkably influence the Sr1−xLaxTiO3 nanocubes’ structure, and their degradation efficiencies were also studied. Undoubtedly, substantial breakthroughs of Sr1−xLaxTiO3 nanocube photocatalysts toward the treatment of organic contaminants from industrial wastewater are expected shortly.

Doping of MoS2 by "Cu" and "V": An Efficient Strategy for the Enhancement of Hydrogen Evolution Activity

To replace Pt-based compounds in the electrocatalytic hydrogen evolution reaction (HER), MoS₂ has already been established as an efficient catalyst. The electrocatalytic activity of MoS₂ is further improved by tuning the morphology and the electronic structure through doping, which helps the band energy position to be modified. Presently, thin sheets of MoS₂ (MoS₂-TSs) are synthesized via a microwave technique. Thin sheets of MoS₂ can outperform nanosheets of MoS₂ in the HER. Further, the efficiency of the thin sheets is improved by doping with different metals like Cu, V, Zn, Mn, Fe, Sn, etc. "Cu"- and "V"-doped MoS₂-TSs are highly efficient for the HER. At a fixed potential of -0.588 V vs RHE, Cu-doped MoS₂ (Cu-MoS₂-TS), V-doped MoS₂ (V-MoS₂-TS), and MoS₂-TS can generate current densities of 327.46, 308.45, and 127.82 mA/cm², respectively. The electrochemically active surface area increases nearly 7.7-fold and 2.5-fold for Cu-MoS₂-TS and V-MoS₂-TS than for MoS₂-TS, respectively. Cu-MoS₂-TS shows exceptionally high electrocatalytic stability up to 140 h in an acidic medium (0.5 M H₂SO₄). First-principles calculations using density functional theory (DFT) are performed, which are well matched with the experimental observations. DFT calculations dictate that after doping with "V" and "Cu" both valance band maxima and conduction band minima are uplifted, which indicates the higher hydrogen-ion-reducing ability of M-MoS₂-TS (M = Cu, V) compared to bare MoS₂-TS.

Photocarrier-assisted photothermocatalysis of Fischer–Tropsch synthesis for the enhanced yield of C2–C4 hydrocarbons over a Co/SrTiO3 catalyst

Photocarrier-assisted photothermocatalysis enhanced the selectivity to C2−C4 hydrocarbons, which can be ascribed to the combined effect of photocatalysis and photothermal catalysis.

The high photocatalytic efficiency and stability of LaNiO3/g-C3N4 heterojunction nanocomposites for photocatalytic water splitting to hydrogen

A binary direct Z-scheme LaNiO₃/g-C₃N₄ nanocomposite photocatalyst consisted with LaNiO₃ nanoparticles and g-C₃N₄ nanosheets was successfully synthesized by means of mechanical mixing and solvothermal methods in order to improve the photocatalytic water splitting activity. The as-prepared materials were characterized by powder X-ray diffraction (XRD), Scanning Electron microscope (SEM), Transmission Electron microscope (TEM), X-ray photoelectron spectroscope (XPS), Fourier Transform Infrared Spectroscopy (FT-IR) and N₂ adsorption–desorption experiments, respectively, demonstrating the formation of interfacial interaction and heterogeneous structure in LaNiO₃/g-C₃N₄ nanocomposites. Under UV-light irradiation, the LaNiO₃/g-C₃N₄ samples which without the addition of any noble metal as co-catalyst behaved enhanced photocatalytic water splitting activity compared with pure LaNiO₃ and g-C₃N₄, owing to the Z-scheme charge carrier transfer pathway. Especially, the LaNiO₃/70%g-C₃N₄ nanocomposite reach an optimal yield of up to 3392.50 µmol g⁻¹ in 5 h and held a maximum H₂ evolution rate of 678.5 µmol h⁻¹ g⁻¹ that was 5 times higher than that of pure LaNiO₃.

Theoretical insights of codoping to modulate electronic structure of [Formula: see text] and [Formula: see text] for enhanced photocatalytic efficiency

[Formula: see text] and [Formula: see text] are well known materials in the field of photocatalysis due to their exceptional electronic structure, high chemical stability, non-toxicity and low cost. However, owing to the wide band gap, these can be utilized only in the UV region. Thus, it's necessary to expand their optical response in visible region by reducing their band gap through doping with metals, nonmetals or the combination of different elements, while retaining intact the photocatalytic efficiency. We report here, the codoping of a metal and a nonmetal in anatase [Formula: see text] and [Formula: see text] for efficient photocatalytic water splitting using hybrid density functional theory and ab initio atomistic thermodynamics. The latter ensures to capture the environmental effect to understand thermodynamic stability of the charged defects at a realistic condition. We have observed that the charged defects are stable in addition to neutral defects in anatase [Formula: see text] and the codopants act as donor as well as acceptor depending on the nature of doping (p-type or n-type). However, the most stable codopants in [Formula: see text] mostly act as donor. Our results reveal that despite the response in visible light region, the codoping in [Formula: see text] and [Formula: see text] cannot always enhance the photocatalytic activity due to either the formation of recombination centers or the large shift in the conduction band minimum or valence band maximum. Amongst various metal-nonmetal combinations, [Formula: see text] (i.e. Mn is substituted at Ti site and S is substituted at O site), [Formula: see text] in anatase [Formula: see text] and [Formula: see text], [Formula: see text] in [Formula: see text] are the most potent candidates to enhance the photocatalytic efficiency of anatase [Formula: see text] and [Formula: see text] under visible light irradiation.

Ba-addition induced enhanced surface reducibility of SrTiO3: implications on catalytic aspects

Surface reducibility engineering is one of the vital tools to enhance the catalytic activity of materials. A heavy redox treatment can be utilized to affect the structure and surface of catalytic materials. Here, we choose SrTiO₃ (STO) with a cubic perovskite structure as a system to induce oxygen vacancies by using nascent hydrogen from NaBH₄ leading to a heavily reduced version of SrTiO₃ (RSTO). To further understand the surface reduction and its dependence on foreign-ion (Ba) incorporation into SrTiO₃, Sr_0.5Ba_0.5TiO₃ (SBTO) and BaTiO₃ (BTO) are synthesized using a facile hydrothermal method. The reduced version of the pristine and mixed oxide shows distinct optical absorptions, indicating oxygen vacancy-mediated reducibility engineering. Detailed CO oxidation experiments suggest the order of activity over the as-prepared and reduced supports as STO > SBTO > BTO and RSBTO > RSTO > RBTO, respectively. The interesting observation of reversal of CO oxidation activity over STO and SBTO after reduction negates the assumption of a similar intensity of reduction on the surfaces of these oxide supports. The fundamental aspect of surface reducibility is addressed using temperature programmed reduction/oxidation (TPR/TPO) and XPS.

Ultrafine CoO nanoparticles as an efficient cocatalyst for enhanced photocatalytic hydrogen evolution

In order to further enhance the performance of photocatalysts, cocatalysts are used to accelerate the photocatalytic reactions. Herein, ultrafine cobalt oxide (CoO) nanoparticles are synthesized through a novel bottom-up strategy and explored as an efficient non-noble cocatalyst to dramatically promote the photocatalytic hydrogen evolution rate of CdS nanorods. CdS/CoO heterostructures, consisting of highly dispersed 3-5 nm CoO nanoparticles anchored on the CdS nanorods, can provide a high photocatalytic hydrogen evolution rate of 6.45 mmol g^-1 h^-1 (∼36 times higher than that of bare CdS nanorods) in the visible-light region (>420 nm). Combined X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy analyses suggest Co-S bond formation between CoO and CdS, which guarantees efficient migration and separation of photogenerated charge carriers. This work provides a new avenue for adopting CoO as an effective cocatalyst for enhanced photocatalytic hydrogen production in the visible-light region.

Bench-Scale Steam Reforming of Methane for Hydrogen Production

The effects of reaction parameters, including reaction temperature and space velocity, on hydrogen production via steam reforming of methane (SRM) were investigated using lab- and bench-scale reactors to identify critical factors for the design of large-scale processes. Based on thermodynamic and kinetic data obtained using the lab-scale reactor, a series of SRM reactions were performed using a pelletized catalyst in the bench-scale reactor with a hydrogen production capacity of 10 L/min. Various temperature profiles were tested for the bench-scale reactor, which was surrounded by three successive cylindrical furnaces to simulate the actual SRM conditions. The temperature at the reactor bottom was crucial for determining the methane conversion and hydrogen production rates when a sufficiently high reaction temperature was maintained (>800 °C) to reach thermodynamic equilibrium at the gas-hourly space velocity of 2.0 L CH4/(h·gcat). However, if the temperature of one or more of the furnaces decreased below 700 °C, the reaction was not equilibrated at the given space velocity. The effectiveness factor (0.143) of the pelletized catalyst was calculated based on the deviation of methane conversion between the lab- and bench-scale reactions at various space velocities. Finally, an idling procedure was proposed so that catalytic activity was not affected by discontinuous operation.