Hydrogen Photoproduction Research Articles

Evolution of the state of copper-based co-catalysts of the Cd0.3Zn0.7S photocatalyst at the photoproduction of hydrogen under action of visible light

The promotion of the photocatalytic activity of the Cd0.3Zn0.7S nanoparticles via deposition of some copper species, such as CuxS and Cu0, as a co-catalyst, in the hydrogen production under visible light irradiation from aqueous solutions of a sacrificial Na2S/Na2SO3 system was studied. The state of the samples was characterized with a wide range of physical methods both in the initial state as well as after their photocatalytic operation. An evolution of both photocatalytic activity and the state of the photocatalyst particles was registered by a set of the physical methods. The highest apparent quantum efficiency and photocatalytic activity which were achieved at illumination by light with λ = 450 nm over the 0.1 wt% CuxS/Cd0.3Zn0.7S sample for the photocatalytic hydrogen evolution from Na2S/Na2SO3 aqueous solutions were 23.1% and 6.4 mmol g−1 h−1, respectively. It was shown that the deposited Cu species undergo the transformation to CuxS during the photocatalytic production of hydrogen, and these are the copper sulfide nanoparticles that increase the activity of the Cd1-xZnxS solid solutions. This statement agrees well with the principle of a constancy of the state of heterogeneous catalysts under their operation in the same reaction media established by G.K. Boreskov in the 1950s.

Optogenetic regulation of artificial microRNA improves H2 production in green alga Chlamydomonas reinhardtii

BackgroundChlamydomonas reinhardtii is an ideal model organism not only for the study of basic metabolic processes in both plants and animals but also the production of biofuels including hydrogen. Transgenic analysis of C. reinhardtii is now well established and very convenient, but inducible exogenous gene expression systems remain under-studied. The most commonly used heat shock-inducible system has serious effects on algal cell growth and is difficult and costly to control in large-scale culture. Previous studies of hydrogen photoproduction in Chlamydomonas also use this heat-inducible system to activate target gene transcription and hydrogen synthesis.ResultsHere we describe a blue light-inducible system with which we achieved optogenetic regulation of target gene expression in C. reinhardtii. This light-inducible system was engineered in a photosynthetic organism for the first time. The photo-inducible heterodimerizing proteins CRY2 and CIB1 were fused to VP16 transcription activation domain and the GAL4 DNA-binding domain, respectively. This scheme allows for transcription activation of the target gene downstream of the activation sequence in response to blue light. Using this system, we successfully engineered blue light-inducible hydrogen-producing transgenic alga. The transgenic alga was cultured under red light and grew approximately normally until logarithmic phase. When illuminated with blue light, the transgenic alga expressed the artificial miRNA targeting photosynthetic system D1 protein, and altered hydrogen production was observed.ConclusionsThe light-inducible system successfully activated the artificial miRNA and, consequently, regulation of its target gene under blue light. Moreover, hydrogen production was enhanced using this system, indicating a more convenient and efficient approach for gene expression regulation in large-scale microalgae cultivation. This optogenetic gene control system is a useful tool for gene regulation and also establishes a novel way to improve hydrogen production in green algae.

Doping or Deposition of NiS on Cd0.3Zn0.7S Photocatalysts: Optimising Photocatalytic Hydrogen Evolution

AbstractThe photocatalytic properties of a Cd0.3Zn0.7S photocatalyst modified either by NiS doping or by supporting NiS on the catalyst surface were studied. The obtained samples were investigated by different characterization techniques, including X‐ray diffraction (XRD), UV/Vis diffuse reflectance spectroscopy (DRS), high‐resolution transmission electron microscopy (HRTEM), and X‐ray photoelectron spectroscopy (XPS). The photocatalytic activity was measured in hydrogen evolution from aqueous solutions of Na2S/Na2SO3 under visible‐light irradiation (λ=450 nm). Nickel modifications on the surface and in bulk led to improvements in the photocatalytic activity compared to the pristine sample. The samples modified in bulk underwent changes in composition and an increase of the catalytic activity during illumination was measured. In contrast, the rate of hydrogen photoproduction for the photocatalysts modified by NiS on the surface did not change appreciably. The highest photocatalytic activity values were 11.2 mmol h−1 g−1 and 12.8 mmol h−1 g−1 for the 0.3 % NiS/Cd0.3Zn0.7S and Ni0.001Cd0.3Zn0.7S1.001 photocatalysts, respectively.

Effect of surface properties of copper-modified commercial titanium dioxide photocatalysts on hydrogen production through photoreforming of alcohols

Deposition of copper on titanium dioxide holds great promise in producing materials with high activity in the photo-production of hydrogen by aqueous reforming of alcohols. This work aims at comparing hydrogen evolution through photoreforming of alcohols over photocatalysts prepared by in situ photodeposition of copper on three TiO2 commercial samples (P25, pure anatase, and pure rutile). The adoption of a single catalyst preparation method and experimental setup allowed to unequivocally ascribe the differences in hydrogen evolution to surface properties of the TiO2 sample tested, thus overcoming the major constraints found in the literature. The resulting samples were extensively characterized by several complementary techniques. Correlations between hydrogen production rates and physical-chemical properties of the samples are discussed. The analyses highlight the major role played by physical size and surface properties of TiO2 particles in determining the morphology, the dispersion of zero-valent copper nanoparticles on the TiO2 surface and, ultimately, the photocatalytic performances. Understanding the correlation between properties and photocatalytic response of copper-modified TiO2 nanoparticles acts as a remarkable lever for the future development of new TiO2-based materials exhibiting high efficiency for hydrogen generation under UV–visible light irradiation.

Evaluation of light energy to H2 energy conversion efficiency in thin films of cyanobacteria and green alga under photoautotrophic conditions

Cyanobacteria and green algae harness solar energy to split water and to fix CO2. Under specific conditions, they are capable of photoproduction of molecular hydrogen (H2). This study compares the light-energy-to-hydrogen-energy conversion efficiency (LHCE) in two heterocystous, N2-fixing cyanobacteria (wild-type Calothrix sp. strain 336/3 and the ΔhupL mutant of Anabaena sp. strain PCC 7120) and in the sulfur-deprived green alga, Chlamydomonas reinhardtii strain CC-124, after entrapment of the cells in thin Ca2+-alginate films. The experiments, performed under photoautotrophic conditions, showed higher LHCEs in the cyanobacteria as compared to the green alga. The highest efficiency of ca. 2.5% was obtained in films of the entrapped ΔhupL strain under low light condition (2.9Wm−2). Calothrix sp. 336/3 films produced H2 with a maximum efficiency of 0.6% under 2.9Wm−2, while C. reinhardtii films produced H2 most efficiently under moderate light (0.14% at 12.1Wm−2). Exposure of the films to light above 16Wm−2 led to noticeable oxidative stress in all three strains, which increased with light intensity. The presence of oxidative stress was confirmed by increased (i) degradation of chlorophylls and some structural carotenoids (such as β-carotene), (ii) production of hydroxylated carotenoids (such as zeaxanthin), and (iii) carbonylation of proteins. We conclude that the H2 photoproduction efficiency in immobilized algae and cyanobacteria can be further improved by entrapping cultures in immobilization matrices with increased permeability for gases, especially oxygen, while matrices with low porosity produced increased amounts of xanthophylls and other antioxidant compounds.

Exploitation of dark fermented effluent of cheese whey by co-culture of Rhodobacter sphaeroides and Bacillus firmus for photo-hydrogen production.

In this study photo-hydrogen production from cheese whey dark fermentation (DF) effluent by the co-culture of Rhodobacter sphaeroides -NMBL-01 and Bacillus firmus - NMBL-03 has been reported. The effect of pH, initial chemical oxygen demand (COD) and the concentration effect of FeSO4.7H2O on photo-hydrogen production have been investigated. The end products of dark fermentation effluent of cheese whey were mainly comprised of soluble organic acids, i.e. butyric acid and lactic acid. The batch process was carried out under light intensity of 2.5 kLux at 32 ± 2oC without any addition of extra carbon and nitrogen source. The single parameter optimization studies revealed optimum pH 6.5, initial COD 4.71 g/L and supplementation of Fe2+ concentration 100 mg/L. The maximum cumulative hydrogen production and yield were found to be 469 ± 45.8 ml H2/L and 146.56 ± 14.31 ml H2/g COD reduced (67.9% reduction in COD) respectively. The mutual interactions among the process parameters were also investigated by three factorial Box-Behnken design of response surface methodology. The optimized experimental values were found concurrent with the calculated values obtained from the theoretical model.

Effect of sulfur source on photocatalytic degradation performance of CdS/MoS2 prepared with one-step hydrothermal synthesis

CdS/MoS2, an extremely efficient photocatalyst, has been extensively used in hydrogen photoproduction and pollutant degradation. CdS/MoS2 can be synthesized by a facile one-step hydrothermal process. However, the effect of the sulfur source on the synthesis of CdS/MoS2via one-step hydrothermal methods has seldom been investigated. We report herein a series of one-step hydrothermal preparations of CdS/MoS2 using three different sulfur sources: thioacetamide, l-cysteine, and thiourea. The results revealed that the sulfur source strongly affected the crystallization, morphology, elemental composition and ultraviolet (UV)–visible-light-absorption ability of the CdS/MoS2. Among the investigated sulfur sources, thioacetamide provided the highest visible-light absorption ability for CdS/MoS2, with the smallest average particle size and largest surface area, resulting in the highest efficiency in Methylene Blue (MB) degradation. The photocatalytic activity of CdS/MoS2 synthesized from the three sulfur sources can be arranged in the following order: thioacetamide>l-cysteine>thiourea. The reaction rate constants (k) for thioacetamide, l-cysteine, and thiourea were estimated to be 0.0197, 0.0140, and 0.0084min−1, respectively. However, thioacetamide may be limited in practical application in terms of its price and toxicity, while l-cysteine is relatively economical, less toxic and exhibited good photocatalytic degradation performance toward MB.

The role of fuel to oxidizer ratio in solution combustion synthesis of TiO2 and its influence on photocatalysis

Abstract

Mesophilic and thermophilic photo-hydrogen production from micro-grinded, enzyme-hydrolyzed maize straws

Photo-fermentative is an endothermic reaction driven by light energy to overcome the energy barrier. This communication conducted photo-fermentation hydrogen tests with micro-grinded, enzyme-hydrolyzed maize straws considering the effects of broth temperature ranging 28.2–54.5 °C. The hydrogen production rate was first increased with broth temperature, peaked at 39.6 °C, and then decreased at higher temperature range. The photo-fermentative process can be approximated as a catalytic reaction with positive activation energy and positive activation entropy, an endothermic, entropy-driven complexation process.

Comparative analyses of H2 photoproduction in magnesium‐ and sulfur‐starved Chlamydomonas reinhardtii cultures

Magnesium (Mg)-deprived Chlamydomonas reinhardtii cells are capable to sustain hydrogen (H2 ) photoproduction at relatively high photosystem II (PSII) activity levels for an extended time period as compared with sulfur (S)-deprived cells. Herein, we present a comparative study of H2 photoproduction induced by Mg and S shortage to unravel the specific rearrangements of the photosynthetic machinery and cell metabolism occurring under the two deprivation protocols. The exhaustive analysis of photosynthetic activity and regulatory pathways, respiration and starch metabolism revealed the specific rearrangements of the photosynthetic machinery and cellular metabolism, which occur under the two deprivation conditions. The obtained results allowed us to conclude that the expanded time period of H2 production upon Mg-deprivation is due to the less harmful effects that Mg-depletion has on viability and metabolic performance of the cells. Unlike S-deprivation, the photosynthetic light and dark reactions in Mg-deprived cells remained active over the whole H2 production period. However, the elevated PSII activity in Mg-deprived cells was counteracted by the operation of pathways for O2 consumption that maintain anaerobic conditions in the presence of active water splitting.

UV and visible hydrogen photo-production using Pt promoted Nb-doped TiO2 photo-catalysts: Interpreting quantum efficiency

Nb-doped titania nanopowders active under UV and visible light were used as supports of platinum and tested in the photo-production of hydrogen using methanol as sacrificial agent in liquid phase. Samples were characterized using X-ray diffraction and photoelectron spectroscopy, UV–vis and photoluminescence spectroscopies, electron paramagnetic resonance, and transmission electron microscopy. The catalytic performance was evaluated taking into account the measurement of the corresponding reaction rates and the computation of the quantum efficiency values. Optimization of the catalytic output upon UV and visible excitation was carried out as a function of the Nb content of the material and using an experimental design taking as factors the methanol:water ratio, and catalyst concentration at liquid phase. The performance of the materials and the optimum for a catalyst containing a 2.5mol% of Nb upon UV, visible light and sunlight was examined. The characterization results concerning both the charge carrier species recombination and the fate of such species at the catalytic surface were used to elucidate the physico-chemical roots for maximizing activity.

Effect of Light/Dark Regimens on Hydrogen Production by Tetraselmis subcordiformis Coupled with an Alkaline Fuel Cell System.

To improve the photoproduction of hydrogen (H2) by a green algae-based system, the effect of light/dark regimens on H2 photoproduction regulated by carbonyl cyanide m-chlorophenylhydrazone (CCCP) was investigated. A fuel cell was integrated into a photobioreactor to allow online monitoring of the H2 evolution rate and decrease potential H2 feedback inhibition by consuming the generated H2 in situ. During the first 15h of H2 evolution, the system was subjected to dark treatment after initial light illumination (L/D=6/9h, 9/6h, and 12/3h). After the dark period, all systems were again exposed to light illumination until H2 evolution stopped. Two peaks were observed in the H2 evolution rate under all three light/dark regimens. Additionally, a high H2 yield of 126±10mLL-1 was achieved using a light/dark regimen of L 9h/D 6h/L until H2 production ceased, which was 1.6 times higher than that obtained under continuous illumination. H2 production was accompanied by some physiological and morphological changes in the cells. The results indicated that light/dark regimens improved the duration and yield of H2 photoproduction by the CCCP-regulated process of Tetraselmis subcordiformis.

Enhanced photo-fermentative hydrogen production of Rhodopseudomonas sp. nov. strain A7 by the addition of TiO2, ZnO and SiC nanoparticles

In order to strengthen photo-fermentative hydrogen production by different photocatalytic nanoparticles, hydrogen production by photo-fermentative bacteria with addition of TiO2, ZnO and SiC nanoparticles in batch culture were investigated in this study. The results indicated that three nanoparticles could improve hydrogen production performance of Rhodopseudomonas sp. nov. strain A7 under respective optimal conditions. The hydrogen yield of 2.81 mol-H2/mol-acetate was obtained when TiO2 nanoparticles with a concentration of 300 mg/L and size of 25 nm. The concentration of ZnO nanoparticles was at 100 mg/L, hydrogen yield reached 2.64 mol-H2/mol-acetate. Compared with TiO2 and ZnO nanoparticles, SiC nanoparticles exhibited greatest potential for enhancing photo-hydrogen production. By addition of nano-SiC with concentration of 200 mg/L which was prepared at temperature of 1500 °C, the maximum hydrogen volume, average hydrogen content and hydrogen yield of strain A7 were achieved at 2272 mL-H2/L-culture, 85.2% and 2.99 mol-H2/mol-acetate, respectively. And hydrogen production was 18.6% higher than that of alone strain A7 without the addition of nanoparticles. Therefore, the addition of SiC nanoparticles is a promising strategy to improve photo-fermentative hydrogen production from wastewater.

Hot Carrier Generation and Extraction of Plasmonic Alloy Nanoparticles.

The conversion of light to electrical and chemical energy has the potential to provide meaningful advances to many aspects of daily life, including the production of energy, water purification, and optical sensing. Recently, plasmonic nanoparticles (PNPs) have been increasingly used in artificial photosynthesis (e.g., water splitting) devices in order to extend the visible light utilization of semiconductors to light energies below their band gap. These nanoparticles absorb light and produce hot electrons and holes that can drive artificial photosynthesis reactions. For n-type semiconductor photoanodes decorated with PNPs, hot charge carriers are separated by a process called hot electron injection (HEI), where hot electrons with sufficient energy are transferred to the conduction band of the semiconductor. An important parameter that affects the HEI efficiency is the nanoparticle composition, since the hot electron energy is sensitive to the electronic band structure of the metal. Alloy PNPs are of particular importance for semiconductor/PNPs composites, because by changing the alloy composition their absorption spectra can be tuned to accurately extend the light absorption of the semiconductor. This work experimentally compares the HEI efficiency from Ag, Au, and Ag/Au alloy nanoparticles to TiO2 photoanodes for the photoproduction of hydrogen. Alloy PNPs not only exhibit tunable absorption but can also improve the stability and electronic and catalytic properties of the pure metal PNPs. In this work, we find that the Ag/Au alloy PNPs extend the stability of Ag in water to larger applied potentials while, at the same time, increasing the interband threshold energy of Au. This increasing of the interband energy of Au suppresses the visible-light-induced interband excitations, favoring intraband excitations that result in higher hot electron energies and HEI efficiencies.

Measuring and interpreting quantum efficiency for hydrogen photo-production using Pt-titania catalysts

A series of samples where platinum is deposited onto titania P25 using a chemical deposition method was tested in the photo-production of hydrogen using methanol as a sacrificial agent. The optimization of the platinum titania contact was analyzed as a function of the synthesis conditions. The catalysts’ structural and electronic properties were measured using a combination of porosimetry, X-ray diffraction, X-ray photoelectron, photoluminescence, and UV–visible spectroscopies, together with a microscopy study of the noble metal particle size distribution and an in situ infrared study of the catalysts under reaction conditions. The measurement of the optical properties of the catalyst suspensions and the subsequent calculation of the true quantum efficiency were used to show that a significant enhancement of ca. 250% can be achieved through the series of Pt-containing catalysts. The study provides solid evidence concerning the physical roots of the photoactivity behavior. For catalysts having equal Pt properties in terms of primary particle size and electron handling capability, a synergy between the noble metal and the oxide support at interface sites is shown to promote the conversion of carboxylate-type surface species into carbon dioxide and maximize the hydrogen yield of the reaction.

Sunlight-Dependent Hydrogen Production by Photosensitizer/Hydrogenase Systems.

We report a sustainable in vitro system for enzyme-based photohydrogen production. The [FeFe]-hydrogenase HydA1 from Chlamydomonas reinhardtii was tested for photohydrogen production as a proton-reducing catalyst in combination with eight different photosensitizers. Using the organic dye 5-carboxyeosin as a photosensitizer and plant-type ferredoxin PetF as an electron mediator, HydA1 achieves the highest light-driven turnover number (TONHydA1 ) yet reported for an enzyme-based in vitro system (2.9×106 mol(H2 ) mol(cat)-1 ) and a maximum turnover frequency (TOFHydA1 ) of 550 mol(H2 ) mol(HydA1)-1 s-1 . The system is fueled very effectively by ambient daylight and can be further simplified by using 5-carboxyeosin and HydA1 as a two-component photosensitizer/biocatalyst system without an additional redox mediator.

Evaluation of the effect of aerobic–anaerobic conditions on photohydrogen and chlorophyll a production by environmental Egyptian cyanobacterial and green algal species

In this study, we tested four algal species (Synechocystis sp. PCC 6803 and three novel algal species isolated from Egyptian paddy rice soil, having high 16S rRNA gene sequence identity to Nostoc spongiaeforme, Parachlorella kessleri SAG 211-11 and Nostoc sp. PCC 7524) under aerobic, anaerobic and 3% CO2-supplemented anaerobic condition. Significant changes in photohydrogen production, morphology, chlorophyll a and protein content/pattern were observed in all species, when grown in these different conditions. H2 production was higher in anaerobic condition in all species with the highest H2 production rate of 4 mmol H2 mg Chla−1 h−1 at 24 h in Synechocystis sp. In contrast, Chla content and protein content decreased (%) in N. spongiaeforme, (29%, 58%), P. kessleri (47%, 7%) and Nostoc sp. (59%, 65%).The anaerobic condition with 3% CO2 stimulated early production of H2 in all species except Synechocystis sp. Our results compared all selected algal species under different growth conditions for the screening of a superior H2-producing algal species that can help to address engineering challenges in the field of large-scale H2 photoproduction by microalgae.

Photoproduction of Hydrogen by Decamethylruthenocene Combined with Electrochemical Recycling

AbstractThe photoinduced hydrogen evolution reaction (HER) by decamethylruthenocene, Cp2*RuII (Cp*=C5Me5), is reported. The use of a metallocene to photoproduce hydrogen is presented as an alternative strategy to reduce protons without involving an additional photosensitizer. The mechanism was investigated by (spectro)electrochemical and spectroscopic (UV/Vis and 1H NMR) measurements. The photoactivated hydride involved was characterized spectroscopically and the resulting [Cp2*RuIII]+ species was electrochemically regenerated in situ on a fluorinated tin oxide electrode surface. A promising internal quantum yield of 25 % was obtained. Optimal experimental conditions— especially the use of weakly coordinating solvent and counterions—are discussed.

Photoproduction of Hydrogen by Decamethylruthenocene Combined with Electrochemical Recycling.

The photoinduced hydrogen evolution reaction (HER) by decamethylruthenocene, Cp2 *RuII (Cp*=C5 Me5 ), is reported. The use of a metallocene to photoproduce hydrogen is presented as an alternative strategy to reduce protons without involving an additional photosensitizer. The mechanism was investigated by (spectro)electrochemical and spectroscopic (UV/Vis and 1 H NMR) measurements. The photoactivated hydride involved was characterized spectroscopically and the resulting [Cp2 *RuIII ]+ species was electrochemically regenerated in situ on a fluorinated tin oxide electrode surface. A promising internal quantum yield of 25 % was obtained. Optimal experimental conditions- especially the use of weakly coordinating solvent and counterions-are discussed.

Low-cost synthesis of titanium dioxide anatase nanoclusters as advanced materials for hydrogen photoproduction

Sub-nm titanium dioxide (TiO2) clusters are synthesized via the hydrolysis of TiCl4 in order to produce clean and surfactant-free oxide surfaces. By controlling the synthesis, stable TiO2 nanoclusters with well-defined size distributions are obtained. The prepared clusters are characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Raman spectroscopy in order to gain information about the size and morphology of the material. Photoresponsive methylene blue dye monitoring and hydrogen production under UV irradiation are described in detail and performed. The rate order of photodegradation and hydrogen photoproduction under UV light irradiation of the samples is increased by decreasing the size of TiO2 nanoparticles from 47 nm to 3 nm. The hydrogen evolution rate of TiO2 nanoclusters with size lower than 5 nm is about 3.03 times and 1.96 times faster than that of 47 nm of TiO2 and 12 nm of TiO2, respectively. The enhanced photocatalytic performance suggests that the ternary TiO2 nanoclusters can serve as a highly efficient catalyst for photodegradation of organic pollutants in aquatic environments and hydrogen production from water splitting.