Photocatalytic Reforming Research Articles

Reasonable regulation of carbon/nitride ratio in carbon nitride for efficient photocatalytic reforming of biomass-derived feedstocks to lactic acid

Photocatalysis provides a promising opportunity for selective oxidation of biomass to high-value chemicals under mild conditions. The key to realize this transformation is to design a cost-effective and environmentally friendly photocatalyst. Here, we report the preparation of a carbon nitride photocatalyst with controllable carbon/nitride (C/N) ratio and its application in the selective photocatalytic synthesis of lactic acid from biomass-derived monosaccharides. Reasonable C/N ratio in the catalyst can significantly enhance the visible light absorption range and accelerate the mobility of photogenerated carriers. The obtained photocatalyst exhibited excellent photocatalytic activity, yielding 76.8% lactic acid. All of the h+,·O2-,·OH and 1O2 are beneficial for lactic acid production, and the·O2- plays a major role. Furthermore, the photocatalyst exhibited excellent reusability and universality. The 1000-fold scale-up experiments indicated that the system has potential for industrial production of lactic acid. Therefore, the present work offers a promising example for photocatalytic reforming of biomass.

Photo‐catalytic reforming of aqueous phase derived from hydrothermal liquefaction of Nostoc ellipsosporum for bio‐hydrogen production

In this study, green fuel (hydrogen energy) was produced from the aqueous phase obtained from the hydrothermally liquefied Nostoc ellipsosporum biomass via photo-catalytic reforming. Initially, algae were cultivated in municipal wastewater and fog medium (80:20) in photo bio-reactor for biomass production. Later the algae biomass was liquefied under varying temperature of 220°C to 320°C at 5Mpa for 60 min. From the results, it was seen that the maximum bio-oil yield was 31 wt% for biomass to solvent ratio of 0.05 g/mL at 300°C. Gas Chromatography-Mass Spectroscopy (GC-MS) analysis of bio-oil showed the presence of hydrocarbons like octadecane, heptadecane, etc. Aqueous phase comprised of hydrogen generating low molecular weight compounds. Photo-catalytic reforming process with 0.1 g of TiO2 catalyst at time of 2 h resulted in hydrogen yield of 27 wt%. Catalyst reusability study resulted in cumulative hydrogen yield of 76 wt% from five consecutive cycles.

Photocatalytic Reforming of Sucrose and Dextrose for Hydrogen Production on Pd/TiO2

AbstractPhotocatalytic reforming of sucrose and dextrose was performed on TiO2 supported Pd (0.25, 0.5, 1.0, 1.5, and 2.0 wt%) catalysts under UV light irradiation. Hydrogen production increases with increasing the sucrose concentration. Semiconductor TiO2 has shown benefit from palladium additions up to about 0.5–1.0 wt%; however, the further metal increase has no benefits. Kinetics study reveals that the apparent reaction rate for hydrogen evolution follows the Langmuir‐Hinshelwood (LH) mechanism. The equilibrium constant (K) determined was 1.078 for 1 %Pd/TiO2, while 2 %Pd/TiO2 exhibited 0.122, which is an order of magnitude less than the former catalyst. Hydrogen yield from dextrose is higher than sucrose under similar reaction conditions. Furthermore, the catalyst pretreated by sodium borohydride displayed higher activity for dextrose reforming than untreated, implying that metallic Pd enhanced hydrogen production.

Macroscopic graphitic carbon nitride monolith for efficient hydrogen production by photocatalytic reforming of glucose under sunlight

Large particulate photocatalysts allow efficient recovery or installation into the substrate, while limiting possible light-catalyst interaction or mass/charge-transfer. In this study, we developed monodisperse organic single-crystal monoliths with controllable dimensions in the range of 10–100 μm. These were prepared on a 10-g scale by a solution-processed molecular cooperative assembly between melamine (M) and trithiocyanuric acid (TCA) and then transformed into the corresponding g-CN (MTCA-CN) by thermal polycondensation. Molecular precursors that are tightly bound in the crystal undergo polycondensation without losing their macroscopic properties depending on the dimensions of MTCA, thereby changing the microstructure, electronic structure, and photocatalytic activity. Such dimensional tunability enables the fulfillment of various catalytic requirements such as particle size, light absorption, charge separation, band edge potential, and mass transfer. As a proof-of-concept, it was shown that MTCA-CN is tailored to have a high rate of evolution of hydrogen (3.19 μmol/h) from glucose via photoreforming under AM1.5G by using MTCA-100 crystals, leading to the formation of g-CN with the more positive highest occupied molecular orbital (HOMO) level. This study highlights the possibility of developing photocatalysts for practical use and obtaining value-added products (VAPs) without losing the photocatalytic activity relevant for wastewater treatment.

Utilizing 2D materials to enhance H2 generation efficiency via photocatalytic reforming industrial and solid waste

Sustainable valorization of industrial and solid wastes by utilizing them as feedstock to generate H2 via the photocatalytic reforming (PR) process holds great promise. It can also be an effective method to treat solid waste that otherwise would require tedious and expensive processes. This approach has the potential to offer energy solutions and form value-added chemicals. In this direction, developing photocatalysts and tuning their properties play an essential role in advancing the H2 generation efficiency. This Review article explores the application of 2D photocatalysts to generate H2 via PR of industrial waste (H2S) and solid waste, such as plastic and biomass. Despite having favorable optoelectronic properties, 2D photocatalysts are not widely employed for the PR process. The latest progress in employing 2D photocatalysts to realize efficient H2 evolution from biomass, plastic, and industrial waste such as H2S is detailed in this Review. A correlation between the properties of 2D photocatalysts with H2 evolution rate is discussed. We also emphasize understanding the mechanism involved in the PR process and the importance of 2D photocatalysts design. Such rational insight aids in further enhancing the H2 generation efficiency by effectively using solid/industrial waste as a feedstock.

Co-hydrothermal gasification of microbial sludge and algae Kappaphycus alvarezii for bio-hydrogen production: Study on aqueous phase reforming

In this study, wastewater obtained from a sewage treatment plant was treated successively by using microbial consortium and macroalgae Kappaphycus alvarezii to generate microbial sludge and algal biomass. The production of green fuel was carried out via co-gasification of microbial sludge and macroalgae Kappaphycus alvarezii for a duration of 60 min, feedstock to solvent ratio (5 to 20 g of feedstock in 200 mL), sludge to algae ratio (ranging from 1:1 to 3:1) and temperature (300–400 °C) respectively. Maximum bio-hydrogen yield was 36.1% and methane yield was 38.4% at a temperature of 360 °C at a feedstock to solvent ratio of 15:200 g/mL and sludge to algae ratio of 2:1 individually. The liquid by product of co-gasification process was later subjected to photocatalytic reforming, resulted in an enhanced hydrogen composition of 61.25%.

TiO2 Photocatalysis for the Transformation of Aromatic Water Pollutants into Fuels

The growing world energy consumption, with reliance on conventional energy sources and the associated environmental pollution, are considered the most serious threats faced by mankind. Heterogeneous photocatalysis has become one of the most frequently investigated technologies, due to its dual functionality, i.e., environmental remediation and converting solar energy into chemical energy, especially molecular hydrogen. H2 burns cleanly and has the highest gravimetric gross calorific value among all fuels. However, the use of a suitable electron donor, in what so-called “photocatalytic reforming”, is required to achieve acceptable efficiency. This oxidation half-reaction can be exploited to oxidize the dissolved organic pollutants, thus, simultaneously improving the water quality. Such pollutants would replace other potentially costly electron donors, achieving the dual-functionality purpose. Since the aromatic compounds are widely spread in the environment, they are considered attractive targets to apply this technology. In this review, different aspects are highlighted, including the employing of different polymorphs of pristine titanium dioxide as photocatalysts in the photocatalytic processes, also improving the photocatalytic activity of TiO2 by loading different types of metal co-catalysts, especially platinum nanoparticles, and comparing the effect of various loading methods of such metal co-catalysts. Finally, the photocatalytic reforming of aromatic compounds employing TiO2-based semiconductors is presented.

Partially reduced Pd single atoms on CdS nanorods enable photocatalytic reforming of ethanol into high value-added multicarbon compound

<h2>Summary</h2> Photocatalytic co-production of high value-added multicarbon compounds and hydrogen from renewable bioethanol is an environmental and long-term approach to industrial activities and remains a great challenge because of the difficulty in bioethanol dehydrogenation. Guided by first-principle simulation, we first synthesized a partially reduced Pd–P₃ single atom (PdPSA) on CdS nanorods with an unoccupied hybrid state of Pd 4d and P 3p via both metal-support interaction effect and Pd–P coordination effect. This unique electronic structure of PdPSA is totally different from highly reduced S-coordinated Pd single atoms or nanoparticles and allows PdPSA-CdS to exhibit a visible-light photocatalytic activity of 35.1 mmol g⁻¹ h⁻¹ for the co-production of high-value-added 1,1-diethoxyethane and H₂ with a selectivity of 100%. Mechanism studies revealed that the unoccupied hybrid states of Pd 4d and P 3p in PdPSA not only greatly promoted the dehydrogenation of ethanol but also promised PdPSA with a high H₂-production activity.

H2 and CH4 production from bio-alcohols using condensed poly(heptazine imide) with visible light

Fully condensed poly(heptazine imide) (PHI) supported with highly dispersed Pt nanoparticles (PtNPs) achieves efficient and persistent H2 and CH4 production by photocatalytic reforming of biomass derived alcohols under visible light irradiation.

CuO@TiO2 and NiO@TiO2 core-shell catalysts for hydrogen production from the photocatalytic reforming of glycerol aqueous solution

Hydrogen production from the photocatalytic reforming of glycerol aqueous solution was performed on the CuO@TiO2, NiO@TiO2, NiO@CuO, and CuO@NiO core-shell nanostructured catalysts under simulated solar light irradiation. These catalysts were prepared by the combination of a modified sol-gel and a precipitation-deposition method using hydroxypropyl cellulose as structural linker and they were characterized by powder X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (UV–Vis DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen physisorption isotherms techniques. The catalysts containing TiO2 as a shell and CuO as core showed much higher activity compared with those formulated with NiO@CuO, CuO@NiO, and bared CuO or NiO nanoparticles. The highest rate of hydrogen production obtained with the CuO@TiO2 catalyst was as high as 153.8 μmol·g−1h-1, which was 29.0, 24.8, 11.2 and 3.2 times greater than that obtained on CuO@NiO, NiO@CuO, TiO2 P25, and NiO@TiO2 catalyst, respectively. For the high active CuO@TiO2 catalyst, after activation of TiO2 with solar light irradiation, the conduction band electrons can be transferred to CuO core through the heterojunction in the core-shell interfaces which led to CuO gradually reduced to Cu2O, favoring the reduction of proton to release hydrogen.

Photocatalytic reforming of aqueous phase obtained from liquefaction of household mixed waste biomass for renewable bio-hydrogen production

In this study, hydrothermal liquefaction of household waste was performed to produce valuable liquid hydrocarbons with aqueous phase as by-product. Photocatalytic reforming of aqueous phase was carried out for hydrogen production. Liquefaction of 15 g waste at temperature of 320 °C and solvent to biomass ratio of 13.33 mL/g produced bio-oil of 32.4 wt% and hydrogen 21 wt% in gas product. Hydrogen production from aqueous phase was studied in presence of various concentrations of activated carbon doped Fe/TiO2 catalyst (0.2–1 wt%). Hydrogen yield was 32 wt% when 0.6 wt% of catalyst was used to reform aqueous phase. To ease of operation in economical manner the reusability study of the catalyst was evaluated and it was found to be active for three consecutive cycles. As outcome of this study, household waste can serve for a whooping amount of hydrogen (53 wt%) production via liquefaction and photocatalytic reforming process.

Lignocellulose-derived monosugars: a review of biomass pre-treating techniques and post-methods to produce sustainable biohydrogen

Biohydrogen (H2) is considered as a prospective energy source for altering of exhausting fossil fuel-based hydrogen in the coming years. Among biomaterials, lignocellulose is the most abundant renewable feedstock for the second generation biohydrogen production through many processes. The conventional microbial fermentation and the photocatalytic reforming have received considerable attention that could convert the monosugars (mainly glucose and xylose) of the lignocellulosic materials into biohydrogen. In general, to obtain these monosugars, the lignocellulosic materials must be pre-treated through various complicated processes. This review focuses on various integrated pre-treating lignocellulosic material techniques and their advantages and disadvantages, including pretreatment, hydrolysis, and detoxification methods to get monosugars. Additionally, the state-of-the-art accomplishments in the post-methods, including microbial fermentation (including photo-fermentation and dark fermentation), microbial electrolysis, and photocatalytic reforming, for further converting monosugars into sustainable biohydrogen, are favorably highlighted. Finally, the perspectives for material pre-treating techniques and future challenges for post-methods to enhance biohydrogen are also discussed and intensified.

Significantly enhanced cocatalyst-free H2 evolution from defect-engineered Brown TiO2

TiO2 is the extensively investigated materials for various photocatalytic reforming and water splitting. Superior stability towards photo-corrosion, appropriate band energy levels driving most photocatalytic reactions, and low-cost production are promising features of TiO2. However, a primary limitation with TiO2 is that it only absorbs ultraviolet light constituting less than 5% of the solar spectrum. In this work, we use a facile, low temperature, vacuum-free, and solution-route synthesis approach to rationally induce oxygen vacancy/Ti3+ defects to reduce the bandgap of TiO2 to 2.0 eV (3.2 eV for pristine white TiO2) to form brown TiO2 with enhanced visible-light absorption. The mechanism of defect formation is systematically deduced from the detailed investigation through Raman spectroscopy, spin-sensitive technique, high-resolution microscopy, and surface analysis. The brown TiO2 yielded 8.1 mmol h−1g−1cat H2 evolution without any cocatalyst under natural sunlight, which is a factor two higher than pristine (white) TiO2. To the best of our knowledge, the observed H2 evolution rate is the highest reported value under natural sunlight for any TiO2-based photocatalyst. This work demonstrates the applicability of brown TiO2 to fabricate large-area photocatalyst panels for the cost-effective production of solar H2.

Metal Single Atom Strategy Greatly Boosts Photocatalytic Methyl Activation and C–C Coupling for the Coproduction of High-Value-Added Multicarbon Compounds and Hydrogen

Photocatalytic reforming of renewable and low-cost biomass is an alternative approach to synthesize high-value-added multicarbon compounds and hydrogen. However, the difficulty in activating the me...

A new concept: Volume photocatalysis for efficient H2 generation __ Using low polymeric carbon nitride as an example

Conversion of solar energy into H2 via photocatalytic reforming of biomass or its derivatives is an attractive technology. However, the photocatalytic reaction efficiency is usually low due to the high recombination of photogenerated electrons and holes. Herein, we demonstrate a new concept and strategy of volume photocatalysis of solid catalysts and construct an efficient reaction system using low polymeric carbon nitride (PCN) as a volume photocatalyst and biomass-derived formic acid as a reactant. In this system, PCN allows the reactant to enter its bulk and in-situ scavenge photogenerated holes, which greatly inhibits the recombination of the electrons and holes. As a result, the left electrons can effectively migrate from the bulk to the surface of PCN to reduce protons/water molecules into hydrogen. The apparent quantum yield (AQY) for photocatalytic hydrogen evolution reaches 51.9% at 400 nm in formic acid reaction system. These findings provide new insights for understanding heterogeneous photocatalysis.

Photocatalytic H2 Evolution from Oxalic Acid: Effect of Cocatalysts and Carbon Dioxide Radical Anion on the Surface Charge Transfer Mechanisms

Photocatalytic reforming of carboxylic acids on co-catalyst-loaded semiconductors is an attractive process for H2 generation that has been studied for years. Experimental support for the surface re...

Mechanistic Insights into Hydrogen Evolution by Photocatalytic Reforming of Naphthalene

Heterogeneous photocatalysis has been widely considered, among other applications, for environmental remediation and hydrogen production. While these applications have been traditionally seen as well-separated areas, recent examples have highlighted the possibility of coupling them. Here, we demonstrate the simultaneous production of H2 and naphthalene removal from aqueous solutions with (unoptimized) photonic efficiencies of 0.97 and 0.33%, respectively, over Pt–TiO2 under simulated sunlight. Photocatalytic and spin-trapping experiments in the presence of a hydroxyl radical and hole scavengers evinced that only the photogenerated holes play a significant role in the oxidation of naphthalene. Isotopic labeling analyses showed that the evolved H2 isotopologues match those of the solvent and that deuterated water (but not deuterated naphthalene) decreases the reaction rate, suggesting its involvement in the rate-determining step. Moreover, the use of Ti18O2 does not lead to the significant formation of 18O-enriched CO2, suggesting that water is the source of the oxygen atoms. Ultimately, by considering the stable and transient reaction intermediates, we propose a plausible reaction pathway. Our work illustrates that environmental remediation can be effectively coupled to solar fuel production, providing a double purpose to photocatalytic reactions, while the mechanistic insights will be of use for the further development of this strategy.

Improving Glycerol Photoreforming Hydrogen Production Over Ag2O-TiO2 Catalysts by Enhanced Colloidal Dispersion Stability.

Solar-driven photocatalytic reforming of biomass-derived resources for hydrogen production offers a sustainable route toward the generation of clean and renewable fuels. However, the dispersion stability of the catalyst particles in the aqueous phase hinders the efficiency of hydrogen production. In this work, a novel method of mixing Ag2O-TiO2 photocatalysts with different morphologies was implemented to promote colloidal dispersion stability, thereby improving hydrogen production performance. A series of Ag2O-TiO2 nanoparticles with different morphologies were synthesized, and their dispersion stabilities in aqueous phase were investigated individually. Two types of Ag2O-TiO2 particles with different morphologies under certain proportions were mixed and suspended in glycerol aqueous solution without adding any dispersant for enhancing dispersion stability while reacting. From the results, photocatalytic hydrogen production was found to be strongly correlated to colloidal dispersion stability. The mixed suspension of Ag2O-TiO2 nanosphere and nanoplate achieved an excellent colloidal dispersion stability without employing any additives or external energy input, and the photoreforming hydrogen production obtained from this binary component system was around 1.1–2.3 times higher than that of the single-component system. From the calculated hydrogen production rate constants between continuous stirring and the binary system, there was only <6% difference, suggesting an efficient mass transfer of the binary system for photoreforming hydrogen production. The proposed method could provide some inspiration to a more energy-efficient heterogeneous catalytic hydrogen production process.

Photocatalytic reforming of glycerol to H2 in a thin film Pt‐TiO2 recirculating photoreactor

AbstractBACKGROUNDWith an increase in global bioenergy production, the ‘biorefinery concept’ has now become a significant focus of research. The desire to achieve efficient conversion of biomass material into both energy and value‐added products requires a combination of technologies and processes. As such, the photocatalytic reforming of feedstocks such as glycerol to hydrogen (H2) has a lot of potential.RESULTSReported here is the first example of a thin film‐based photocatalytic system capable of achieving H2 evolution using a glycerol feedstock. Using a titania (TiO2) sol–gel, glass columns were coated with a thin TiO2 layer before using photodeposition to add platinum (Pt) as a co‐catalyst. The coated columns were assembled into a simple yet effective recirculating system which used low power UV irradiation. Under optimum conditions (two coated columns and a 40 mL min−1 flow rate), a steady state of 0.9 μmol min−1 H2 with a photonic efficiency [ηphoton (%)] of 10.22 % was achieved. Furthermore, only one column showed flaking and loss of coating whereas the remaining columns were stable for the duration of the study, which equated to &gt; 100 h of experimental testing including replicates and determining optimal parameters.CONCLUSIONH2 evolution via photocatalytic glycerol reforming in a Pt‐TiO2 thin film catalyst recirculating system has been demonstrated under UV irradiation and ambient conditions. The system developed highlights that it is both catalyst development and reactor engineering that are required to continue to advance the field of photocatalysis. © 2020 The Authors. Journal of Chemical Technology &amp; Biotechnology published by John Wiley &amp; Sons Ltd on behalf of Society of Chemical Industry.

Systematic study of H2 production from catalytic photoreforming of cellulose over Pt catalysts supported on TiO2

Abstract Hydrogen (H2) production from photocatalytic reforming of cellulose is a promising way for sustainable H2 to be generated. Herein, we report a systematic study of the photocatalytic reforming of cellulose over Pt/m-TiO2 (i.e. mixed TiO2, 80% of anatase and 20% of rutile) catalysts in water. The optimum operation condition was established by studying the effect of Pt loading, catalyst concentration, cellulose concentration and reaction temperature on the gas production rate of H2 (rH2) and CO2 (rCO2), suggesting an optimum operation condition at 40 °C with 1.0 g·L−1 of cellulose and 0.75 g·L−1 of 0.16-Pt/m-TiO2 catalyst (with 0.16 wt% Pt loadting) to achieve a relatively sound photocatalytic performance with rH2 = 9.95 μmol·h−1. It is also shown that although the photoreforming of cellulose was operated at a relatively mild condition (i.e. with an UV-A lamp irradiation at 40 °C in the aqueous system), a low loading of Pt at ~ 0.16 wt% on m-TiO2 could promote the H2 production effectively. Additionally, by comparing the reaction order expressed from both rH2 (a1) and rCO2 (a2) with respect to cellulose and water, the possible mechanism of H2 production was proposed.