Photocatalytic Reforming Research Articles

Ultrathin Porous Carbon Nitride Anchored with Pt Nanoclusters for Synergistic Enhancement of Hydrogen Production in Alkaline Photocatalytic Polyester Reforming.

Photocatalytic reforming (PR) of polyester waste, fueled by renewable sources like solar energy, offers a sustainable method for producing clean H2 and valuable by-products under mild conditions. The design of high-performance photocatalyst plays a pivotal role in determining the efficacy of an alkaline polyester PR system, influencing H2 generation activity and selectivity. Here, ultrathin porous carbon nitride nanosheets (UP-CN) loaded with Pt nanoclusters (Pt NCs, average diameter of 1.7nm) with uniform Pt NCs distribution are introduced. The resulting Pt NCs/UP-CN catalyst can accelerate charge and mass transfer while providing additional active sites, achieving superior H2 generation rates of 11.69mmol gcat -1 h-1 and 2923mmol gPt -1 h-1 under AM 1.5 light, which nine times higher than that of Pt nanoparticles-bulk graphitic carbon nitride composite (1.29mmol gcat -1 h-1 and 258mmol gPt -1 h-1) as counterpart. This performance also surpasses that of previously reported carbon nitride-based and TiO2-based photocatalysts. Moreover, the density functional theory calculations reveal a significant reduction in the energy barrier for the water dissociation step (H2O + * → *H + OH) at the interface between UP-CN and anchored Pt NCs, showcasing the synergistic effect between Pt NCs and UP-CN. This catalytic system also exhibits universality across various polyester plastics.

Mild‐Condition Photocatalytic Reforming of Methanol‐Water by a Hierarchical, Asymmetry Carbon Nitride

AbstractAs a reproducible intermediate for hydrogen (H2) and carbon cycling, methanol mixed with water (H2O) in a ratio of 1 : 1 can multiply the outcome of green H2 generation via Photocatalytic reforming of methanol‐H2O (PRMW). Hitherto, low‐energy and mild‐condition PRMW remains a serious challenge. Here, the amino acid‐derived carbon nitrides (ACN) were synthesized supramolecular precursor strategy for PRMW and achieved excellent performance (H2, 35.6 mmol h−1 g−1; CO2, 11.5 mmol h−1 g−1) under sunlight at 35 °C. It was revealed that the surface‐terminating carboxyl groups (−COOH) promote the dark dehydrogenation of methanol on MetCNx to form methoxy (*OCH3) and methylol (*CH2OH) simultaneously, with the hydroxyl (*OH) generated by photostimulated H2O oxidation promotes the C−H activation of formaldehyde, then leads the whole reaction into the formation of CO2 and three H2. The extended light absorption, enhanced charge separation and transport, and efficient surface reaction improve photocatalytic efficiency.

Mild-Condition Photocatalytic Reforming of Methanol-Water by a Hierarchical, Asymmetry Carbon Nitride.

As a reproducible intermediate for hydrogen (H2) and carbon cycling, methanol mixed with water (H2O) in a ratio of 1 : 1 can multiply the outcome of green H2 generation via Photocatalytic reforming of methanol-H2O (PRMW). Hitherto, low-energy and mild-condition PRMW remains a serious challenge. Here, the amino acid-derived carbon nitrides (ACN) were synthesized supramolecular precursor strategy for PRMW and achieved excellent performance (H2, 35.6 mmol h-1 g-1; CO2, 11.5 mmol h-1 g-1) under sunlight at 35 °C. It was revealed that the surface-terminating carboxyl groups (-COOH) promote the dark dehydrogenation of methanol on MetCNx to form methoxy (*OCH3) and methylol (*CH2OH) simultaneously, with the hydroxyl (*OH) generated by photostimulated H2O oxidation promotes the C-H activation of formaldehyde, then leads the whole reaction into the formation of CO2 and three H2. The extended light absorption, enhanced charge separation and transport, and efficient surface reaction improve photocatalytic efficiency.

Solar‐Driven Reforming of Lignocellulosic Biomass to Renewable Biohydrogen: A Review

AbstractTo date, humans are looking for suitable energy sources to meet the global demand for fuels. Among many candidates, biohydrogen (bio‐H2), a future fuel perspective, is expected to grow critically and receive considerable attention to replace fossil fuels. This review focuses on biohydrogen production via post‐method photocatalytic reforming of ideal feedstock and abundant lignocellulosic biomass. Renewable biomass precursors are used without net greenhouse gas emissions. This idea holds great promise as a sustainable and environmentally friendly energy solution. In particular, many saccharide substrates, including monosaccharides, disaccharides, polysaccharides, etc., have been used as sacrificial reagents in photocatalytic reforming over the past few decades. Among the various substrates, cellulose has attracted worldwide attention since it is the most abundant polymeric biomass resource that can be obtained from many sources. Following, photo‐reforming of renewable lignocellulosic biomass, which aligns with the requirements of sustainable development, is successfully proposed. The overall catalytic efficiency will be discussed regarding the biohydrogen evolution rate (mmol gcat−1 h−1). Finally, the review concluded with challenges and potential opportunities to enhance biohydrogen are also given.

Green Syngas Production from Natural Lignin, Sunlight, and Water over Pt-Decorated InGaN Nanowires.

Transformation of lignin to syngas can turn waste into treasure yet remains a tremendous challenge because of its naturally evolved stubborn structure. In this work, light-driven reforming of natural lignin in water for green syngas production is explored using Pt-decorated InGaN nanowires. The spectroscopic characterizations, isotope, and model compound experiments, as well as density function theory calculation, disclose that among a variety of groups including aromatic ring, -OH, -OCH3, -C3H7 with complex chemical bonds of O-H, C-H, C-C, C-O, etc., InGaN nanowires are cooperative with Pt for preferably breaking the C-O bond of the rich O-CH3 group in lignin to liberating ⋅CH3 by photogenerated holes with a minimum dissociation energy of 2.33 eV. Syngas are subsequently yielded from the continuous evolution of ⋅CH3 and ⋅OH from photocatalytic reforming of lignin in water. Together with the superior optoelectronic attributes of Pt-decorated InGaN nanowires, the evolution rate of syngas approaches 43.4 mol ⋅ g-1 ⋅ h-1 with tunable H2/CO ratios and a remarkable turnover number (TON) of 150, 543 mol syngas per mol Pt. Notably, the architecture demonstrates a high light efficiency of 12.1 % for syngas generation under focused light without any extra thermal input. Outdoor test ascertains the viability of producing syngas with the only inputs of natural lignin, water, and sunlight, thus presenting a low-carbon route for synthesizing transportation fuels and value-added chemicals.

Photocatalytic Reforming of Ethanol in the Liquid Phase Using a Ternary Composite of Rh/TiO2/g-C3N4 as a Catalyst.

Photocatalytic reforming of ethanol provides an effective way to produce hydrogen energy using natural and nontoxic ethanol as raw material. Developing highly efficient catalysts is central to this field. Although traditional semiconductor/metal heterostructures (e.g., Rh/TiO2) can result in relatively high catalyst performance by promoting the separation of photoinduced hot carriers, it will still be highly promising to further improve the catalytic performance via a cost-effective and convenient method. In this study, we developed a highly efficient photocatalyst for ethanol reformation by preparing a ternary composite structure of Rh/TiO2/g-C3N4. Hydrogen is the main product, and the reaction rate could reach up to 27.5 mmol g-1 h-1, which is ∼1.41-fold higher than that of Rh/TiO2. The catalytic performance here is highly dependent on the wavelength of the light illumination. Moreover, the photocatalytic reforming of ethanol and production of hydrogen were also dependent on the Rh loading and g-C3N4:TiO2 ratio in Rh/TiO2/g-C3N4 composites as well as the ethanol content in the reaction system. The mechanism of the enhanced hydrogen production in Rh/TiO2/g-C3N4 is determined as the improvement in the separation of photoinduced hot carriers. This work provides an effective photocatalyst for ethanol reforming, largely expanding its application in the field of renewable energy and interface science.

Green Syngas Production from Natural Lignin, Sunlight, and Water over Pt‐Decorated InGaN Nanowires

AbstractTransformation of lignin to syngas can turn waste into treasure yet remains a tremendous challenge because of its naturally evolved stubborn structure. In this work, light‐driven reforming of natural lignin in water for green syngas production is explored using Pt‐decorated InGaN nanowires. The spectroscopic characterizations, isotope, and model compound experiments, as well as density function theory calculation, disclose that among a variety of groups including aromatic ring, −OH, −OCH3, −C3H7 with complex chemical bonds of O−H, C−H, C−C, C−O, etc., InGaN nanowires are cooperative with Pt for preferably breaking the C−O bond of the rich O−CH3 group in lignin to liberating ⋅CH3 by photogenerated holes with a minimum dissociation energy of 2.33 eV. Syngas are subsequently yielded from the continuous evolution of ⋅CH3 and ⋅OH from photocatalytic reforming of lignin in water. Together with the superior optoelectronic attributes of Pt‐decorated InGaN nanowires, the evolution rate of syngas approaches 43.4 mol ⋅ g−1 ⋅ h−1 with tunable H2/CO ratios and a remarkable turnover number (TON) of 150, 543 mol syngas per mol Pt. Notably, the architecture demonstrates a high light efficiency of 12.1 % for syngas generation under focused light without any extra thermal input. Outdoor test ascertains the viability of producing syngas with the only inputs of natural lignin, water, and sunlight, thus presenting a low‐carbon route for synthesizing transportation fuels and value‐added chemicals.

Sodium-doped carbon nitride for visible light-driven photocatalytic reforming lignocellulose into H2 and chemicals

The photocatalytic reforming of lignocellulose and water (H2O) splitting has emerged as a promising method for generating sustainable hydrogen (H2), offering a solution to the global energy crisis. However, the efficiency of the photocatalytic process is often hampered by the low utilization of sunlight and the recombination of photogenerated charge carriers on the photocatalysts. A sodium-doped graphitic carbon nitride (g-C3N4-Na) was developed through a straightforward co-pyrolysis technique, and the sodium doping not only boosts the light absorption capacity of g-C3N4 but also promotes the separation and migration of photogenerated charge carriers. Subsequently, the H2 evolution rate of g-C3N4-Na6 is 14 times higher than that of pure g-C3N4. Additionally, under visible light irradiation, we have efficiently produced several value-added chemicals (such as mannose, rhamnose, galacturonic acid, glucuronic acid, glucose, and arabinose) from α-cellulose oxidation. This research paves the way for developing new strategies for sustainable and efficient H2 production, contributing to the alleviation of energy crisis and fostering a more sustainable future.

Hydrogen evolution via photocatalytic reforming of biomass with palladium nanoparticles decorated g-C3N4 nanosheets

Fossil fuel depletion and environmental toxins have made photocatalytic H2 production of paramount significance. A novel and unique technique for producing sustainable H2 and valorizing biomass using infinite solar energy is biomass photoreformation. Nevertheless, this environmentally friendly method is usually linked to severe reaction circumstances, insufficient selectivity, and restricted biomass conversion. Here, we present a novel one-pot photoreformation technique over porous g-C3N4 nanosheets surface-modified with Pd nanoparticles to convert d-glucose to H2. By stacking the g-C3N4 photocatalyst into a 2D nanosheet structure, some of its inherent drawbacks can be mitigated. Furthermore, the inclusion of noble metal nanoparticles in these g-C3N4 nanosheet structures could significantly boost existing photocatalytic activity. The majority of solar radiation is composed of visible light, which makes up 45% of it, and ultraviolet light, which makes up 5%. Therefore, our focus has been on utilizing abundant visible light to facilitate biomass reformation. After 4 h of continuous irradiation, our composite photocatalyst exhibited exceptional visible light activity; its H2 evolution was 1839.84 μmolg−1h−1, or about 27 times higher than that of undoped g-C3N4 nanosheets. The effectiveness of three different Pd loadings on g-C3N4 nanosheets for glucose reforming was examined. In the quest for an improved H2 evolution visible light active photocatalyst, g-C3N4 nanosheets made at various pyrolysis temperatures loaded with optimized Pd weight percentage were also examined.

Enhanced π-electron transport in graphitic carbon nitride (g-C3N4) by constructing biochar-welded donor-acceptor (D-A) configuration for photocatalytic conversion of biomass

g-C3N4 has broad prospects in photocatalytic upgrading of biomass but suffers from the large exciton binding energy and high charge recombination rate. Herein, we integrated the biomass-derived carbocyclic rings with heptazine units via π-conjugation, constructing biochar-welded electron donor (D)-acceptor (A) structures in g-C3N4. This structure can induce intrinsic driving forces that promoted electron delocalization and transport. Meanwhile, the interlayer π-π stacking interaction of the carbocyclic rings provided a channel for electrons to migrate on the vertically layered structure. The g-C3N4 with biochar-welded D-A configuration exhibited an improved yield of 87.52 % for xylonic acid from biomass monosaccharide. The mechanism study confirmed the dominant role of superoxide radicals (·O2-) and distinguished singlet oxygen (1O2) from the generation path, demonstrating the supporting role of 1O2 originated from an energy transfer process. This work proposed a universal strategy to construct g-C3N4-based photocatalysts with D-A configuration to achieve efficient photocatalytic reforming of biomass.

Efficient photocatalytic reforming of cellulose for H2 production enabled by oxygen-vacancy rich SrMoO4/palygorskite nanocomposite

Photocatalytic reforming of biomass into hydrogen along with the simultaneous production of high-value chemicals, plays a significant role in advancing a sustainable economy. A major challenge in this process is the effective utilization of photogenerated holes while simultaneously preventing the rapid recombination of photoinduced carriers, which is crucial for optimizing solar-to-hydrogen conversion efficiency. In this study, an exquisite oxygen-rich vacancy (OV) plasmonic SrMoO4/phosphor acidized palygorskite (H-Pal) nanocomposite was prepared for efficient photocatalytic H2 evolution while producing high value-added lactic acid (LA) simultaneously. Results showed that the integration of local surface plasmon resonance (LSPR) effect and OV enhanced the photothermal catalytic conversion of cellulose reaching as high as 87%. Notably, the selectivity of LA reached as high as 31% while the H2-evolution efficiency reached 906 μmol•g-1•h-1. The local thermal effect improved the conversion efficiency of cellulose, and the OV in SrMoO4 introduced instantaneous Lewis acid sites during light irradiation, which improved the selectivity for LA. Moreover, the formation of an S-scheme SrMoO4-OV/H-Pal heterostructure effectively inhibited the recombination of photogenerated electron-hole pairs and maintained a high redox potential. This work demonstrates a promising strategy for efficient photocatalytic H2-evolution, coupled with production of high-valuable chemicals from biomass resources by taking advantage of clay materials.

Efficient visible light photocatalytic green hydrogen production from Dy2O3 combined with nitrogen-deficient g-C3N4

The efficient construction of heterojunction photocatalysts has a crucial significance in achieving the decomposition of water for hydrogen generation. This work successfully prepared nitrogen-deficient g-C3N4 (ND-g-C3N4) and combined it with dysprosium oxide (Dy2O3) through high-temperature calcination to create a type II heterojunction photocatalyst (Dy2O3/ND-g-C3N4). Notably, under visible light, the Dy2O3/ND-g-C3N4 photocatalyst demonstrated impressive hydrogen production rates in both ethylene glycol and glucose solutions. Specifically, the photocatalyst achieved H2 generation rates of 463.256 and 510.305 μmol⋅g−1⋅h−1 in ethylene glycol and glucose solutions, respectively. And the quantum yield could be up to 21.76% and 23.96%, respectively. Furthermore, the photocatalytic reforming of glucose for H2 production yielded valuable intermediate products. The f-shell layer in the Dy2O3 had a significant function in enhancing photocatalytic hydrogen production efficiency. This improvement was attributed to the ability of the f-shell layer to capture excited electrons, thereby decreasing the rate of recombination of exciton pairs.

Band Structure Tuning via Pt Single Atom Induced Rapid Hydroxyl Radical Generation toward Efficient Photocatalytic Reforming of Lignocellulose into H2.

Photocatalytic lignocellulose reforming for H2 production presents a compelling solution to solve environmental and energy issues. However, achieving scalable conversion under benign conditions faces consistent challenges including insufficient active sites for H2 evolution reaction (HER) and inefficient lignocellulose oxidation directly by photogenerated holes. Herein, it is found that Pt single atom-loaded CdS nanosheet (PtSA-CdS) would be an active photocatalyst for lignocellulose-to-H2 conversion. Theoretical and experimental analyses confirm that the valence band of CdS shifts downward after depositing isolated Pt atoms, and the slope of valence band potential on pH for PtSA-CdS is more positive than Nernstian equation. These characteristics allow PtSA-CdS to generate large amounts of •OH radicals even at pH 14, while the capacity is lacking with CdS alone. The employment of •OH/OH- redox shuttle succeeds in relaying photoexcited holes from the surface of photocatalyst, and the •OH radicals can diffuse away to decompose lignocellulose efficiently. Simultaneously, surface Pt atoms, featured with a thermoneutral , would collect electrons to expedite HER. Consequently, PtSA-CdS performs a H2 evolution rate of 10.14 µmol h-1 in 1m KOH aqueous solution, showcasing a remarkable 37.1-fold enhancement compared to CdS. This work provides a feasible approach to transform waste biomass into valuable sources.

Photocatalytic reforming of ethanol to produce hydrogen: Effect of anatase doped with NiO on products and reaction pathways

Photocatalytic hydrogen production is of great significance for the transformation of energy system. To improve the hydrogen production performance, nano-photocatalysts including pure TiO2 and NiO-TiO2 were prepared by sol-gel method in this paper. To unravel reaction intermediates and pathways, the adsorption experiments and photocatalytic reaction of ethanol over the photocatalysts were carried out in combination with in situ DRIFTS technique, and the main products in the photocatalytic process were detected through gas chromatography. The results showed that 2NiO-TiO2 as the optimum photocatalyst can yield the maximum H2 rate at 20.10 mmol g−1 h−1. For the adsorption of ethanol on TiO2 and 2NiO-TiO2, the molecular form of ethanol is more dominant than the dissociated form, and CH3CH2OTi is more easily generated on 2NiO-TiO2 than pure TiO2. The hydrogen production pathway changes by doping with NiO, reducing the production of acetic acid and aldehydes and producing the important intermediate CH2CHOTi.

Rational Design of S-Scheme Heterojunction toward Efficient Photocatalytic Cellulose Reforming for H2 and Formic Acid in Pure Water.

Photocatalytic cellulose reforming usually requires harsh conditions due to its sluggish kinetics. Here, a hollow structural S-scheme heterojunction of ZnSe and oxygen vacancy enriched TiO2 , namely, h-ZnSe/Pt@TiO2 , is designed and fabricated, with which the photocatalytic reforming of cellulose for H2 and formic acid is realized in pure water. H2 and formic acid productivity of 1858 and 372µmol g-1 h-1 and a steady H2 evolution for 300 h are achieved with α-cellulose. Comparable photocatalytic activity can also be achieved using various cellulose sources. It is experimentally proven that the photogenerated charge transfer follows an S-scheme mechanism, which not only promotes the charge separation but also preserves the higher reductive and oxidative abilities of the ZnSe and TiO2 , respectively. Furthermore, the polyhydroxy species produced during cellulose degradation are favored to adsorb on the oxygen vacancy enriched TiO2 surface, which promotes the photocatalytic reforming process and is accounted to the preservation of formic acid as the major solution-phase product. In addition, sequential reactions of oxidation of aldehydes and elimination of formic acid of the cellulose degradation process are revealed. This work provides a photocatalytic strategy to sustainably produce hydrogen and value-added chemicals from biomass under the most environmentally benign condition, i.e., pure water.

Recent Advances in the Conversion of Methane to Syngas and Chemicals via Photocatalysis

AbstractAs a primary constituent of natural gas and shale gas, direct conversion of methane has attracted significant attention due to its potential to reduce energy consumption and CO2 emissions. Compared with thermal catalysis, photocatalysis has the capacity to transcend thermodynamic constraint and enable the conversion of sustainable solar energy into chemical energy under mild reaction condition, which contributes to optimize the utilization of methane. In this review, we undertake a comparative analysis of various strategies for photocatalytic methane conversion to syngas and chemicals, including photocatalytic reforming of methane, photocatalytic partial oxidation of methane and photocatalytic coupling of methane. The distinct reaction systems with corresponding catalysts and underlying mechanisms are expounded in detail to foster a profound comprehension of solar‐driven methane conversion. Finally, the challenges and prospectives in photocatalytic methane conversion are discussed.

Unraveling the effect of low Cu2O loading on P25 TiO2 and its self-reduction during methanol photoreforming

Using noble metal-free catalysts is highly promising for sunlight-driven photocatalytic H2 production. Copper compounds have gained considerable interest in this regard. Cu2O/semiconductor composites exhibit superior photocatalytic activity compared to individual compounds. This study focuses on different CuXO/TiO2 composites synthesized via chemical reduction, using Cu2O weight ratios ranging from 1 to 0.05 concerning the TiO2 source. Characterization techniques were employed, including XRD, SEM, XPS, UV–Vis DRS, PL, and TRMC. Surface modification of TiO2 with Cu species (CuO, Cu2O, and Cu0) was observed during the photocatalytic reforming of methanol under simulated solar light. By loading small amounts of CuXO (0.05–0.1%) on TiO2, the highest H2 production and methanol mineralization were achieved, along with the formation of metallic copper. The coexistence of the Cu species and TiO2 facilitated the effective separation of photogenerated electrons and holes, promoting the photoreduction of protons and photooxidation of methanol, respectively.

Photocatalytic Reforming of Biomass Components Using Systems Based on Graphite-Like Carbon Nitride: A Review

Photocatalytic Reforming of Biomass Components Using Systems Based on Graphite-Like Carbon Nitride: A Review

Mechanism insights for efficient photocatalytic reforming of formic acid with tunable selectivity: Accelerated charges separation and spatially separated active sites

Photocatalytic reforming of formic acid (FA) is considered a promising energy conversion method for producing solar fuels and valuable chemical feedstocks to achieve the carbon-neutral goal. However, the application of FA photocatalytic reforming has been restricted by the low efficiency and relatively fixed selectivity due to limited knowledge about the reaction mechanism. Herein, we study the efficient CdS/W2N3 photocatalyst system for photoreforming of FA with tunable selectivity to realize the conversion of products from H2 to syngas under simulated sunlight. Widely tunable CO:H2 ratios between 0 and 2.18 along with a record-high apparent quantum yield (AQY) of 61.00% (H2) and 76.84% (syngas) at 420 nm have been demonstrated. Both theoretical investigation and experimental results show that intrinsic N vacancies and spatially separated active sites are vital factors in achieving tunable selectivity. This work provides a insightful information to construct and understand the photocatalytic system for efficiently reforming of FA with tunable selectivity.

Efficient visible-light-driven CH4 reforming by covalent organic frameworks: Enhancing the activity of cadmium-based catalyst

Dry reforming of methane to prepare synthesis gas is an innovative and practical solution to the current energy crisis as well as environmental issues such as the greenhouse effect. However, the traditional thermocatalytic methane reforming process has limitations, such as high energy consumption and harsh reaction conditions. Here, a novel strategy for the conversion of CO2 and CH4 is reported: the fast and efficient preparation of CO and H2 using solar energy at ambient temperature. In this work, the covalent organic framework (COF) composite is prepared with the hydrothermal method, and its physicochemical properties are studied using different characterization methods. Then, CdS@COF (CCF) is creatively used in the photocatalytic system of CO2-CH4, and the interaction law between the coupling of different mass fractions of COF and CdS and the performance of photocatalytic CH4 reforming is explored. Notably, the CdS@COF (5/5) catalyst shows the best performance in the photocatalytic conversion of CO2 and CH4, with CO and H2 yields of 640μ mol g−1 and 113.24μ mol g−1, respectively. Additionally, the structure–activity relationship between CdS@COF and the photocatalytic conversion of CO2 and CH4 is studied by density functional theory calculation (DFT), including the demonstration of Z-shaped heterojunctions, the adsorption and activation of CO2 and CH4, and the state density of the composites. Finally, based on isotopic tracer experiments, a possible mechanism for CdS@COF photocatalytic reforming of CH4 is proposed. This work provides new research ideas for designing organic semiconductor composites and achieving carbon neutrality.