Characterization of a β-1,4-glucosidase from a newly isolated strain of Pholiota adiposa and its application to the hydrolysis of biomass

The highly efficient β-1,4-glucosidase (BGL)-secreting strain, Pholiota adiposa SKU0714, was isolated and identified based on its morphological features and sequence analysis of internal transcribed spacer (ITS) rDNA. P. adiposa BGL (PaBGL), which contained a carbohydrate moiety, was purified to homogeneity from P. adiposa culture supernatants by 2-step chromatography on DEAE and Sephacryl gel filtration columns. The relative molecular weight of PaBGL was 60 kDa by SDS-PAGE or 59 kDa by size exclusion chromatography, indicating that the enzyme is a monomer. The pH and temperature optima for hydrolysis were 5.0 and 65 °C, respectively. PaBGL showed the highest activity towards p-nitrophenyl-β-d-glucopyranoside (V_max = 4390 U mg protein⁻¹, K_m = 2.23 mol m⁻³) and cellobiose (V_max = 3460 U mg protein⁻¹, K_m = 5.60 mol m⁻³) ever reported. Its internal amino acid sequences showed homology with hydrolases from the glycoside hydrolase family 3 (GH3), indicating that PaBGL is a member of the GH3 family. The hydrolysis of rice straw using a commercial cellulase, Celluclast^® 1.5L, resulted in a higher saccharification yield with the addition of PaBGL than with Novozyme 188. PaBGL may be a good candidate for applications that convert biomasses to biofuels and chemicals.     

Bio-hydrogen production and the F0F1-ATPase activity of Rhodobacter sphaeroides: Effects of various heavy metal ions

Rhodobacter sphaeroides MDC 6521 isolated from Arzni mineral springs in Armenia is able to produce bio-hydrogen (H₂) in anaerobic conditions upon illumination in the presence of various metal ions. The significant aspect in regulation of H₂ production by these bacteria and its energetics is the requirement for F₀F₁-ATPase, the main membrane enzyme responsible for generation of proton motive force under anaerobic conditions. In order to determine the mediatory role of F₀F₁ in H₂ production, the effects of various metal ions (Mn²⁺, Mg²⁺, Fe²⁺, Ni²⁺, and Mo⁶⁺) on N,N′-dicyclohexylcarbodiimide inhibited ATPase activity of R. sphaeroides membrane vesicles were investigated. These ions in appropriate concentrations considerably enhanced H₂ production, which was not observed in the absence of Fe²⁺, indicate the requirement for Fe²⁺. The R. sphaeroides membrane vesicles demonstrated significant ATPase activity. In the absence of Fe²⁺ inhibition (∼80%) of ATPase activity was observed, which was increased by addition of metal ions. A higher ATPase activity was detected in the presence of Fe²⁺ (80 μM) and Mo⁶⁺ (16 μM). These results indicate a relationship between the F₀F₁-ATPase activity and H₂ production that might be a significant pathway to provide novel evidence of a requirement for F₀F₁-ATPase in H₂ production by R. sphaeroides.     

Inhibition by the ionic strength of hydrogen production from the organic fraction of municipal solid waste

Composition of the Organic Fraction of Municipal Solid Waste (OFMSW) in organic compounds and inorganic ions is highly variable and might impact the microbial activity in dark fermentation processes. In this study, the effect of the total amount of inorganic ions on fermentative hydrogen production was investigated. Batch experiments were carried out at pH 6 and under a temperature of 37 °C. A freshly reconstituted organic fraction of municipal solid waste (OFMSW) was used as model substrate. At low concentrations in ammonium or chloride ions (2.9–5.1 g L⁻¹, respectively), the hydrogen yield reached a maximum of 40.8 ± 0.5. mLH₂.gVS⁻¹ and 25.1 ± 5.6 mLH₂.gVS⁻¹. In contrast, at high total ionic concentrations of ammonium and chloride (11.1–35.5 g L⁻¹ respectively), a strong inhibition of the fermentative microbial activity and more particularly hydrogen production, was observed. When considering the ionic strength of each ion, the effects of ammonia, chloride or a mixture of different ions (Na⁺, K⁺, H⁺, Li⁺, NH₄⁺, Mn²⁺, NH₄⁺, Mg²⁺, Cl⁻, PO₄³⁻, Br⁻, I⁻, SO₄²⁻) showed very similar inhibitory trends regardless the type of ion or the composition of the ionic mixture. A threshold inhibitory value of the ionic strength was estimated at 0.75 ± 0.13 M with a substantial impact on the fermentative activity from 0.81 ± 0.12 M, with hydrogen yields of 18.1 ± 3.3 and 6.2 ± 4.1 mLH₂.gVS⁻¹, respectively. Microbial community composition was also significantly impacted with a specific decrease in relative abundance of hydrogen-producing bacteria from the genus Clostridium sp. at high ionic strength.     

Investigation of the electrocatalytic performance for oxygen evolution reaction of Fe-doped lanthanum nickelate deposited on pyrolytic graphite sheets

Perovskite-type metal oxides have emerged as important materials in renewable energy because the high electrocatalytic performance for oxygen evolution reaction (OER). Hence, we perform a study on the electrocatalytic properties of LaNi_1-xFe_xO₃ (x = 0.0, 0.3, 0.6, and 0.9 mol%) for OER, mainly analyzing the influence provoked by the incorporation of Fe³⁺ in the lattice as well as the use of pyrolytic graphite sheet (PGS) as a potential substrate for electrocatalysis. These perovskites were synthesized by the co-precipitation method. The thin film electrodes were prepared depositing the obtained powders on PGS substrates via drop-casting. Depending on the Fe³⁺ level, structural changes and morphological modifications were identified for these materials. The highest electrocatalytic activity for OER was detected for LaNi_0.4Fe_0.6O₃. Besides the low charge transfer resistance, LaNi_0.4Fe_0.6O₃ exhibited a lower overpotential (439 mV) and a smaller Tafel slope (52 mV dec⁻¹) than the LaNiO₃ (465 mV and 76 mV dec⁻¹).     

Harvesting microalgal biomass using magnesium coagulation-dissolved air flotation

Coagulation with magnesium was found to be more effective for harvesting microalgae Chlorella zofingiensis with dissolved air flotation (DAF) than the use of Fe³⁺, Al³⁺ or chitosan, and the required coagulant dosage was in the order Mg²⁺ < chitosan < Al³⁺ < Fe³⁺. The Mg²⁺ dosage required depended on the growth phases and culture medium characteristics. An early exponential culture required the highest Mg²⁺ dosage (226 mg g⁻¹), while a late stationary culture required the lowest dosage (36 mg g⁻¹). HPO₄²⁻ and CO₃²⁻ in the culture medium competed with the microalgal cells for Mg²⁺ and increased the Mg²⁺ dosage necessary. No Mg²⁺ addition was required to harvest the freshwater microalgae Scenedesmus dimorphus grown in a pond with tap water with a high Mg²⁺ concentration or the marine microalgae Nannochloropsis sp. The critical coagulation pH ranged between 10.8 and 11.8, with a lower pH requirement at a higher Mg²⁺ concentration. Magnesium hydroxide precipitated with the harvested biomass; however, over 99.5% of the precipitated Mg²⁺ was recovered by washing the biomass with 0.1 M HCl. Microalgal harvesting with Mg²⁺ did not introduce extrinsic coagulant; thus, neither the biomass nor the medium was contaminated.     

Enhancement of bio-hydrogen generation by spirulina via an electrochemical photo-bioreactor (EPBR)

The biological production of hydrogen by microalgae is considered as an advantageous process. However, its yields are sometimes limited. To go beyond this limit, the improvement of the H₂ generation rate by Spirulina was studied via an electrochemical photo-bioreactor (EPBR). This EPBR led to hydrogen evolution rates of up to 27.49 and 13.37 mol of H₂.d⁻¹.m⁻³ for the anode and cathode chambers, respectively, under 0.3 V voltage and ~2.5 mA current. These results represent about a 4-fold increase compared to the H₂ production rate recorded without the application of a voltage. This increase in bio-hydrogen production is correlated with a drop in the concentration of NADPH. The Electrochemical Sequential Batch Reactor (ESRB) provided a more interesting total production rate which was 2.65 m³ m⁻³ d⁻¹, compared to the batch mode, which gave 1.2 m³ m⁻³.d⁻¹. The results show, for the first time, the boosting effect of the voltage on the metabolism of H₂ production by the Spirulina strain.     

Hydrogen production in reactors: The influence of organic loading rate,inoculum and support material

Hydrogen production was evaluated in two thermophilic structured bed (USBR) reactors. USBR1was inoculated with auto-fermented sugarcane vinasse and low-density polyethylene cubes were used as support material. USBR2 was inoculated with anaerobic sludge from an up-flow anaerobic sludge blanket (UASB) reactor treating sugarcane vinasse, and polyurethane foam matrices was used as support material. The reactors were operated in parallel with sugar cane molasses at organic loading rate (OLR) from 30 to 120 g COD L⁻¹d⁻¹ during 45 days. Hydrogen production was detected during the whole operational period, with maximum values of 1123 mL H₂ d⁻¹L⁻¹ and 2041 mL H₂ d⁻¹L⁻¹ for USBR1 and USBR2, respectively. The number of gene copies encoding for Fe-hydrogenase was higher in USBR2 for all OLR applied. DNA sequences related to Thermoanaerobacterium and Clostridium sensu stricto were predominant in USBR1. In USBR2, in addition to these microorganisms, Lactobacillus, Pseudomonas and Thermotuga, and sequences with low frequency of abundance (<5%) involved directly and indirectly in hydrogen production were also present. The taxonomical and functional more diverse inoculum of USBR2 was associated with a higher hydrogen production. Besides fermentation, an unknown metabolism was relevant in USBR2, revealing the importance of physiological characterization of the microbial community present.     

Enhanced hydrogen storage capacity of NiAl-layered double hydroxide modified with Tb3Fe5O12 nanostructures

Under ultrasonic irradiation, the porous Tb₃Fe₅O₁₂ (TFO) and Nickel Aluminum layer double hydroxide (NiAl-LDH) were synthesized by investigation the effect of sonication time. Synthesis of TFO was conducted in the presence of tetradentate Schiff-base ligand H₂salophen, [N,N′-bis(salicylidene)-1,2-phenylenediamine] as complexing agent to size controlling and further growth prevention of crystals. The resultant nanocomposites of TFO/NiAl-LDH used as novel active compounds for applying in hydrogen storage strategies. Comprehensively, the hydrogen capacitance after 15 cycles was displayed on the pure NiAl-LDH and TFO materials about 115 and 334 mAhg⁻¹ respectively. It demanded the maximum capacitance for Tb₃Fe₅O₁₂/NiAl-LDH nanocomposites was 451 mAhg⁻¹, which was higher than the initial NiAl-LDH structure. It was exposed from the spillover effect that; the endorsed electrochemical hydrogen storage (EHS) performance is ascribed to the reaction of the redox pair of Fe³⁺/Fe²⁺ at the active sites throughout the EHS procedure. This work delivers a novel plan and potential sorption electrode materials to progress the intrinsic action of layered compounds.     

Investigation of structural,electrical and electrochemical properties of La0.6Sr0.4Fe0.8Mn0.2O3-δ as an intermediate temperature solid oxide fuel cell cathode

La_0.6Sr_0.4Fe_0.8Mn_0.2O₃ (LSFM) compound is synthesized by sol-gel method and evaluated as a cathode material for the intermediate temperature solid oxide fuel cell (IT-SOFC). X-ray diffraction (XRD) indicates that the LSFM has a rhombohedral structure with R-3c space group symmetry. The XRD patterns reveal very small amount of impurity phase in the LSFM and Y₂O₃-stabilized ZrO₂ (YSZ) mixture powders sintered at 600, 700, 800 and 850 °C for a week. The maximum electrical conductivity of LSFM is about 35.35 S cm⁻¹ at 783 °C in the air. The oxygen chemical diffusion coefficients, D_Chem, are increased from 1.39 × 10⁻⁶ up to 1.44 × 10⁻⁵ cm² s⁻¹. Besides, the oxygen surface exchange coefficients, k_Chem, are obtained to lie between 2.9 × 10⁻³ and 1.86 × 10⁻² cm s⁻¹ in a temperature range of 600–800 °C. The area-specific resistances (ASRs) of the LSFM symmetrical cell are 7.53, 1.53, 1.13, 0.46 and 0.31 Ω cm² at 600, 650, 700, 750 and 800 °C respectively, and related activation energy, E_a, is about 1.23 eV.     

Effect of synthesis methods on magnetic Kans grass biochar for enhanced As(III,V) adsorption from aqueous solutions

Magnetic biochar is increasingly known as a multi-functional material and the appropriate synthesis method further increase its efficient applications. In this study, the effects of synthesis methods on the fabrication of Kans grass straw/biochar (KGS/KGB) with Fe³⁺/Fe²⁺ by chemical co-precipitation and subsequently pyrolyzing at 500 °C for 2 and 4 h were studied in details, and compared their As(III, V) adsorption potentials under different operating conditions. Magnetic biochars (MKGB3 and MKGB4) prepared from KGS revealed of superior Fe₃O₄ loading, higher As(III, V) adsorption efficiency and saturation magnetization (45.7 Am² kg⁻¹) than that of KGB (MKGB1 and MKGB2). Moreover, Thermogravimetric analysis (TGA) demonstrated three stages of decomposition and the MKGB3 and MKGB4 generated higher residual mass (>60%) at stage 3 (1000 °C) due to greater Fe₃O₄ composite in biochar matrix and turned to be thermally more stable. As(III) and As(V) adsorption equilibrium data well fitted in Langmuir model and followed the order: MKGB4 > MKGB3 > MKGB2 > MKGB1. The maximum As(III) and As(V) adsorption capacities were about 2.0 mg g⁻¹ and 3.1 mg g⁻¹, respectively. The data best fitted in pseudo-second-order (R² > 0.99) rather than pseudo-first-order kinetics model indicating of more complex mechanism. The adsorption of As(III) and As(V) was found to decrease with increasing in ionic strength of competing ions and PO₄³⁻ was found to strongly inhibit arsenic adsorption. Highest desorption was achieved at pH 13.5 using NaOH. This study suggests that selective adsorbent synthesis method could be useful to prepare effective adsorbent for toxic metals immobilization.     

Thermodynamic and kinetic properties of calcium hydride

Calcium hydride has shown great potential as a hydrogen storage material and as a thermochemical energy storage material. To date, its high operating temperature (above 800 °C) has not only hindered its opportunity for technological application but also prevented detailed determination of its thermodynamics of hydrogen sorption. In addition, calcium metal suffers from high volatility, high corrosivity from Ca (and CaH₂), slow kinetics of hydrogen sorption, and the solubility of Ca in CaH₂. In this work, a literature review of the wide-ranging thermodynamic properties of CaH₂ is provided along with a detailed experimental investigation into the thermodynamic properties of molten and solid CaH₂. The thermodynamic values of hydrogen release from both molten and solid CaH₂ were determined as ΔH_des (molten CaH₂) = 216 ± 10 kJ mol⁻¹.H₂, ΔS_des (molten CaH₂) = 177 ± 9 J K⁻¹ mol⁻¹.H_2, which equates to a 1 bar hydrogen equilibrium temperature for molten CaH₂ of 947 ± 65 °C. Similarly, in the solid-state: ΔH_des (solid CaH₂) = 172 ± 12 kJ mol⁻¹.H₂, ΔS_des (solid CaH₂) = 144 ± 10 J K⁻¹ mol⁻¹.H₂. Moreover, the activation energy of hydrogen release from CaH₂ was also calculated using DSC analysis as E_a = 203 ± 12 kJ mol⁻¹. This study provides the first thermodynamics for the Ca–H system in over 60 years, providing more accurate data on this emerging energy storage material.     

Impact of regulated pH on proto scale hydrogen production from xylose by an alkaline tolerant novel bacterial strain, Enterobacter cloacae DT-1

A hydrogen producing facultative anaerobic alkaline tolerant novel bacterial strain was isolated from crude oil contaminated soil and identified as Enterobacter cloacae DT-1 based on 16S rRNA gene sequence analysis. DT-1 strain could utilize various carbon sources; glycerol, CMCellulose, glucose and xylose, which demonstrates that DT-1 has potential for hydrogen generation from renewable wastes. Batch fermentative studies were carried out for optimization of pH and Fe²⁺ concentration. DT-1 could generate hydrogen at wide range of pH (5–10) at 37 °C. Optimum pH was; 8, at which maximum hydrogen was obtained from glucose (32 mmol/L), when used as substrate in BSH medium containing 5 mg/L Fe²⁺ ion. Decrease in hydrogen partial pressure by lowering the total pressure in the fermenter head space, enhanced the hydrogen production performance of DT-1 from 32 mmol H₂/L to 42 mmol H₂/L from glucose and from 19 mmol H₂/L to 33 mmol H₂/L from xylose. Hydrogen yield efficiency (HY) of DT-1 from glucose and xylose was 1.4 mol H₂/mol glucose and 2.2 mol H₂/mol xylose, respectively. Scale up of batch fermentative hydrogen production in proto scale (20 L working volume) at regulated pH, enhanced the HY efficiency of DT-1 from 2.2 to 2.8 mol H₂/mol xylose (1.27 fold increase in HY from laboratory scale). 84% of maximum theoretical possible HY efficiency from xylose was achieved by DT-1. Acetate and ethanol were the major metabolites generated during hydrogen production.     

Associated effects of storage and mechanical pre-treatments of microalgae biomass on biomethane yields in anaerobic digestion

The pre-treatment of microalgae cell walls is known to be a key factor to enhance methane (CH₄) yields during anaerobic digestion. This study investigated the combined effects of two different biomass storage methods and physical pre-treatments on the anaerobic digestion for three different microalgae species. Acutodesmus obliquus, Chlorella vulgaris and Chlorella emersonii were cultivated in 80 L sleevebag photobioreactors (batch mode), and then subjected to different storage (cooling and freezing) and pre-treatment methods prior to anaerobic digestion using the biochemical methane potential (BMP) test. A. obliquus was selected to evaluate pre-treatment methods for further experimentation. Significantly higher CH₄ yields of cooled (4 °C) A. obliquus biomass were achieved through ultrasonication (+53% CH₄) and wet-milling (+51% CH₄). These methods were then applied in follow-up experiments to cooled (4 °C) biomass of C. emersonii and A. obliquus. Ultrasonication again led to significantly higher CH₄ yields for A. obliquus biomass (323 dm³ kg⁻¹ CH₄ yield calculated at standard gas conditions of 273 K, and 101.5 kPa per unit volatile solids, +41% CH₄), and C. emersonii biomass (308 dm³ kg⁻¹; +35% CH₄). In a third experiment series, frozen A. obliquus and C. vulgaris biomass were thawed prior to pre-treatment and BMP-testing. Among all BMP tests, the highest CH₄ yields were achieved with untreated, freeze-thawed C. vulgaris biomass (406 dm³ kg⁻¹); pre-treatment did not enhance CH₄ yields for C. vulgaris, but for A. obliquus (ultrasonication +20%). Pre-treatment was more effective for cooled than freeze-thawed microalgal biomass and combined effects acted strain dependently.     

Thermophilic hydrogen and methane production from sugarcane stillage in two-stage anaerobic fluidized bed reactors

This study evaluated the feasibility of H₂ and CH₄ production in two-stage thermophilic (55 °C) anaerobic digestion of sugarcane stillage (5,000 to 10,000 mg COD.L⁻¹) using an acidogenic anaerobic fluidized bed reactor (AFBR-A) with a hydraulic retention time (HRT) of 4 h and a methanogenic AFBR (AFBR-S) with HRTs of 24 h–10 h. To compare two-stage digestion with single-stage digestion, a third methanogenic reactor (AFBR-M) with a HRT of 24 h was fed with increasing stillage concentrations (5,000 to 10,000 mg COD.L⁻¹). The AFBR-M produced a methane content of 68.4 ± 7.2%, a maximum yield of 0.30 ± 0.04 L CH₄.g COD⁻¹, a production rate of 3.78 ± 0.40 L CH₄.day⁻¹.L⁻¹ and a COD removal of 73.2 ± 5.0% at an organic loading rate (OLR) of 7.5 kg COD.m⁻³.day⁻¹. In contrast, the two-stage AFBR-A system produced a hydrogen content of 23.9 ± 5.6%, a production rate of 1.30 ± 0.16 L H₂.day⁻¹.L⁻¹ and a yield of 0.34 ± 0.08 mmol H₂.g CODap⁻¹. Additionally, the decrease in the HRT from 18 h to 10 h in the AFBR-S favored a higher methane production, improving the maximum methane content (74.5 ± 6.0%), production rate (5.57 ± 0.38 L CH₄.day⁻¹.L⁻¹) and yield (0.26 ± 0.06 L CH₄.g COD⁻¹) at an OLR of 21.6 kg COD.m⁻³.day⁻¹ (HRT of 10 h) with a total COD removal of 70.1 ± 7.1%. Under the applied COD of 10,000 mg L⁻¹, the two-stage system showed a 52.8% higher energy yield than the single-stage anaerobic digestion system. These results show that, relative to a single-stage system, two-stage anaerobic digestion systems produce more hydrogen and methane while achieving similar treatment efficiencies.     

Hydrogen evolution by photocatalytic decomposition of water under ultraviolet–visible irradiation over K2La2Ti3−xMxO10+δ perovskite

New layered transition metal substituted perovskite-type oxides K₂La₂Ti_3−xM_xO_10+δ (M = Fe, Ni, W; δ varies with different M) were synthesized with high-temperature solid state reaction, and characterized with X-ray diffraction (XRD) and ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS). The photocatalytic activity of these catalysts was studied under ultraviolet and visible light irradiation. The results indicated that substitution of a part of Ti⁴⁺ with Fe³⁺ and W⁶⁺ resulted in a marked increase in water splitting activity. The activity of these catalysts for water splitting decreased in the order: Fe³⁺ > W⁶⁺ > Ni²⁺ ≥ no substitution. The effect of different amounts of Ti⁴⁺ with Fe³⁺ substitution on water splitting was also evaluated. The highest hydrogen evolution was observed for perovskite composition having a Fe:Ti molar ratio of 1:14 (1:12 weight ratio) and this hydrogen evolution was over 4 times higher than the Fe-free K₂La₂Ti₃O₁₀ composition. Fe was also found to be a promising component for photo activity under visible light irradiation. Finally, the effect of Na₂S/Na₂SO₃ system as the sacrificial agent on the photocatalytic activity was also studied.     

Calcium-doped carbon fabrication for improving bioH2 and bioCH4 production

Carbon-based materials have been well demonstrated to significantly improve biohydrogen (bioH₂) and biomethane (bioCH₄) production. However, the use of the same material for two-phase anaerobic digestion requires further investigation. In this study, three calcium-doped magnetic biochars (Ca-MBCs) with Fe²⁺ (0.01, 0.05 and 0.1 mol/L) and calcium lignosulphonate (CL) were prepared to promote H₂ and CH₄ yields. Material characterization revealed that the specific surface area was significantly increased and Fe ions were successfully attached to the BCs. All three Ca -MBCs can effectively raise H₂ yield, especially Ca-MBC2 (0.05 mol/L Fe²⁺), and the highest H₂ yield of 1050 mL was obtained. Under optimal conditions, the cumulative H₂ (37 °C, pH 6.0) and CH₄ yields (37 °C, pH 7.0) were 948 mL and 1599 mL, respectively, which were 64.9% and 40.8% higher than those of the control group. Ca-MBC2 promoted the activity of butyric acid fermentative bacteria at the H₂ evolution phase, raising the relative abundance of Clostridium; At the methanogenisis phase, the content of coenzyme F420 was increased, and Ca-MBC2 could change the methanogens dominant strain, strengthen the dominant strain position of Methanolinea, and raise the relative abundances of H₂- and acetic acid-trophic strains of Methanoregula, Methanosaeta, and Methanosarcina.     

Promotional Effect of ZrO2 on supported FeCoK Catalysts for Ethylene Synthesis from catalytic CO2 hydrogenation

This study is to convert renewable H₂ and increasingly concerned CO₂ to ethylene or C₂H₄ over Fe_3.33Co_1.67K₅/ZrO₂ and Fe_3.33Co_1.67K₅/Al₂O₃ catalysts. The ZrO₂ support provides amounts of surface oxygen vacancies (OVs) as well as stable and rich surface hydroxyl groups (-OH), which promotes the Fe_3.33Co_1.67K₅/ZrO₂ catalysts with 5% Fe and Co loadings to achieve C₂H₄ space time yield (STY) of 0.064 mmol_C2H4∙m⁻²_cat∙h⁻¹ at 290 °C and 2.0 MPa, while the Fe_3.33Co_1.67K₅/Al₂O₃ catalysts only reach C₂H₄ STY of 0.009 mmol_C2H4∙m⁻²_cat∙h⁻¹ at 330 °C and 2 MPa Fe_3.33Co_1.67K₅/ZrO₂ catalysts are very promising for converting the captured CO₂ and renewable H₂ to highly demanded C₂H₄. This work not only provides a guideline for developing efficient catalysts but also advances the mechanistic understanding of catalytic CO₂ hydrogenation.     

Bamboo-like N-doped carbon tubes encapsulated Co2P–Fe2P derived from zeolitic imidazolate framework as an efficient trifunctional electrocatalyst for water splitting and Zn-air batteries

The development of high-performance and stable trifunctional electrocatalysts is a pressing challenge for the practical application of water splitting and regenerative Zn-air batteries. Herein, bamboo-like N-doped carbon tubes encapsulated Co₂P–Fe₂P nanoparticles (CoFe-PN/C) was fabricated via a facile template-sacrificial approach by using CoZn-ZIF trapping Fe³⁺ (CoFeZn/C) as the precursor. The incorporation of Fe³⁺ was achieved by the one-pot synthesis approach during crystallization of ZIF, which led to the generation of the unique bamboo-like tube structure under the condition of simultaneous phosphating and carbonization. Benefiting from the large surface area, the optimized electronic structure of active sites and the unique bamboo-like nanotube, the resultant CoFe-PN/C can be used as the trifunctional electrocatalyst possessing a small overpotential at 10 mA cm⁻² for the HER (178 mV) and OER (300 mV), as well as a high half-wave potential of 0.884 V for ORR (40 mV more positive than that of commercial 20 wt% Pt/C). Moreover, the self-designed CoFe-PN/C||CoFe-PN/C alkaline electrolyzer driving 50 mA cm⁻² only need operating potential of 1.84 V and the maximum discharge power density of the CoFe-PN/C-assembled ZABs could achieve 152.0 mW cm⁻², superior to those of Pt/RuO₂ couple. This work will facilitate the development and application of trifunctional electrocatalysts based on bi-transition metallic phosphides for energy conversion and storage technology.     

Improvement of biohydrogen production from brewery wastewater: Evaluation of inocula,support and reactor

This work explores the production of biohydrogen from brewery wastewater using as inoculum a culture produced by natural fermentation of synthetic wastewater and Klebsiella pneumoniae isolated from the environment. Klebsiella pneumoniae showed good performance as inoculum, as evaluated using assays of between 9 and 16 cycles, with durations of 12 and 24 h, carbohydrate concentrations from 2.79 to 7.22 g L⁻¹, and applied volumetric organic loads from 2.6 to 12.6 g carbohydrate L⁻¹ day⁻¹. The best results were achieved with applied volumetric organic loads of 12.6 g carbohydrate L⁻¹ day⁻¹ and cycle length of 12 h, resulting in mean volumetric productivity of 0.88 L H₂ L⁻¹ day⁻¹, maximum molar flow of 10.80 mmol H₂ h⁻¹, and mean yield of 0.70 mol H₂ mol⁻¹ glucose consumed. The biogas H₂ content was between 18 and 42%, while the mean organic compounds removal and carbohydrate conversion efficiencies were 23 and 81%, respectively. The inoculum produced by natural fermentation was not viable.     

Elaboration,physical and photo-electrochemical properties of NiCr2O4. Application to hydrogen production under visible irradiation

The physical and photoelectrochemical characterization of NiCr₂O₄, prepared by sol gel route, were investigated to be applied for the H₂ production. The thermal gravimetry (TG) indicates that the single phase is formed above 530 °C as confirmed by X-ray diffraction (XRD). The Nano powder crystallizes in a tetragonal structure with lattice constants: a = 8.3276 Å and c = 8.5542 Å and a particle size of 63 nm, smaller than that obtained by Transmission Electronic Microscopy (TEM) analysis; the latter gives sizes between 80 and 150 nm, indicating crystallites agglomeration. The variation of the dielectric constant (ε) with temperature gives a relative value of 26 at 10 kHz. A direct optical transition at 1.79 eV is determined from the diffuse reflectance spectroscopy assigned to Cr³⁺ octahedrally coordinated. The thermal variation of the conductivity shows that 3d-electrons are localized and the data are modelled by a lattice-polaron hopping with an activation energy of 0.17 eV. The dependence of the interfacial capacitance on the potential (C⁻² - E) indicates p-type behavior with a flat band potential (E_fb) of −0.23 VSCE and holes density (N_A) of 5.88 × 10¹⁶ cm⁻³. The potential of the conduction band (−1.85 V_SCE) is below the H₂O/H₂ level (∼-1.2 V_SCE), allowing a spontaneous H₂-release under visible light. The O₂ evolution occurs at high over-voltage as shown from the intensity-potential (J-E) characteristic in Na₂SO₄ solution (0.1 M) and a hole scavenger was used to preclude the photo corrosion. The NiCr₂O₄ mass, pH and the hole scavenger (S₂O₃²⁻ and NO₂⁻) were optimized. The H₂ volume reached 65 μmol with an evolution rate of 8.6 μmol g⁻¹ min⁻¹, liberated under optimized conditions {1.2 g catalyst L⁻¹, pH ∼9 with thiosulfate S₂O₃²⁻ [10⁻³ M]}.