Optimization of combined (acid + thermal) pretreatment for fermentative hydrogen production from Laminaria japonica using response surface methodology (RSM)

In the present work, a combined (acid + thermal) pretreatment was applied for the enhanced fermentative H₂ production (FHP) from Laminaria japonica. Various pretreatment conditions including HCl concentrations, heating temperatures, and reaction times were optimized via response surface methodology (RSM) with a Box-Behnken design (BBD). Through regression analysis, it was found that H₂ yield was well fitted by a quadratic polynomial equation (R² = 0.97), and the HCl concentration was the most significant factor influencing FHP. The desirable pretreatment conditions found were HCl concentration of 4.8%, temperature of 93 °C, and reaction time of 23 min, under which H₂ yield reached to 159.6 mL H₂/g dry cell weight (dcw). The main organic acids produced were acetic and butyric acids that related closely with H₂ production. The concentration of hydroxymethylfurfural (HMF), a byproduct formed during the pretreatment process, showed an inverse relationship with H₂ yield, indicating that pretreatment conditions for the H₂ production from L. japonica were successfully optimized, by increasing the hydrolysis rate of the feedstock and also reducing the formation of HMF.     

Theoretical investigation of adsorption and dissociation of H2 on (ZrO2)n (n=1-6) clusters

The structure, vibration, and electronic structure of H₂ molecule adsorbed on (ZrO₂)_n (n = 1-6) clusters were investigated with density functional theory. We found that H₂ is easily absorbed on the top Zr atoms of (ZrO₂)_n (n = 1-6) clusters. The Zr₅O₁₀H₂ cluster has the lowest binding energies in the Zr_nO_2nH₂ (n = 1-6) clusters. By analyzing vibrational frequency and Mulliken charge, the H-O and Zr-H bonds were found to be formed in different sized Zr_nO_2nH₂ clusters. The dissociation mechanism of H₂ shows that the charge transfers from (ZrO₂)_n cluster to H₂ due to the important role of the orbital hybridization between the cluster and H₂ molecule. With increasing the number of H₂ molecule adsorbed on (ZrO₂)_n clusters, the adsorption favors to the sites with low coordinate number, and these adsorption modes present a symmetrical tendency.     

Synthesis of (CuIn)xCd2(1−x)S2 photocatalysts for H2 evolution under visible light by using a low-temperature hydrothermal method

A new series visible-light driven photocatalysts (CuIn)_xCd_2(1−x)S₂ was successfully synthesized by a simple and facile, low-temperature hydrothermal method. The synthesized materials were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area measurement, X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible spectroscopy (UV–Vis DRS). The results show that the morphology of the photocatalysts changes with the increase of x from 0.01 to 0.3 and their band gap can be correspondingly tuned from 2.37 eV to 2.30 eV. The (CuIn)_xCd_2(1−x)S₂ nanocomposite show highly photocatalytic activities for H₂ evolution from aqueous solutions containing sacrificial reagents, SO₃²⁻ and S²⁻ under visible light. Substantially, (CuIn)_0.05Cd_1.9S₂ with the band gap of 2.36 eV exhibits the highest photocatalytic activity even without a Pt cocatalyst (649.9 μmol/(g h)). Theoretical calculations about electronic property of the (CuIn)_xCd_2(1−x)S₂ indicate that Cu 3d and In 5s5p states should be responsible for the photocatalytic activity. Moreover, the deposition of Pt on the doping sample results in a substantial improvement in H₂ evolution than the Pt-loaded pure CdS and the amount of H₂ produced (2456 μmol/(g h)) in the Pt-loaded doping system is much higher than that of the latter (40.2 μmol/(g h)). The (CuIn)_0.05Cd_1.9S₂ nanocomposite can keep the activity for a long time due to its stability in the photocatalytic process. Therefore, the doping of CuInS₂ not only facilitates the photocatalytic activity of CdS for H₂ evolution, but also improves its stability in photocatalytic process.     

Effect of Ce on the structural features and catalytic properties of La(0.9−x)CexFeO3 perovskite-like catalysts for the high temperature water-gas shift reaction

La_(0.9−x)Ce_xFeO₃ perovskite-like catalysts were investigated for the production of hydrogen from simulated coal-derived syngas via the water-gas shift reaction in the temperature range 450-600 °C and at 1 atm. These catalysts exhibited higher activity at high temperatures (T ≥ 550 °C), compared to that of a commercial high temperature iron-chromium catalyst at 450 °C. Addition of a low Ce content (x = 0.2), has little influence on the formation of the LaFeO₃ perovskite structure, but enhances catalytic activity especially at high temperatures with 19.17% CO conversion at 550 °C and 40.37% CO conversion at 600 °C. The LaFeO₃ perovskite structure and CeO₂ redox properties play an important role in enhancing the water-gas shift activity. Addition of a high Ce content (x = 0.6) inhibits the formation of the LaFeO₃ perovskite structure and decreases catalyst activity.     

Development of an improved method of cultivation to obtain high biomass of the red alga Gelidiella acerosa (Gelidiales, Rhodophyta) in the open sea

This study describes a suspended stone (SS) method developed for in situ propagation of Gelidiella acerosa. The biomass yield potentials with various growth parameters were studied and compared to the floating raft method that was regarded as a superior method for Gelidiella propagation. The biomass of G. acerosa produced by the SS method consistently increased from the first to the fourth harvest (r = 0.940; P < 0.01) and ranged from 528 to 3645 g fresh wt m⁻². For the raft method biomass increased from the first to the third harvest (977-1288 g fresh wt m⁻²) and then decreased in the fourth harvest (953 g fresh wt m⁻²). The DGR values of the SS method increased exponentially (r = 0.865; P < 0.05) from the first to the fourth harvest (1.33-2.62%) and these values significantly differed from those obtained from the raft method in the second to fourth harvest (P < 0.001) but did not significantly differ in the first harvest (P > 0.05). The biomass of an individual plant harvested from the SS method was significantly higher (P < 0.001) than those obtained for the raft method at all four harvests. The frequency distribution of weight of an individual plant in the SS method also constantly increased in successive harvests and 5% of the plantings in the fourth harvest attained a biomass of 200-250 g fresh wt. The in situ propagation of this species through the SS method described in this study could be a viable option for conservation and large-scale farming in the sea.     

Synthesis of nano-crystalline (Ba0.5Sr0.5)Co0.8Fe0.2O3−δ cathode material by a novel sol–gel thermolysis process for IT-SOFCs

Nano-crystalline (Ba_0.5Sr_0.5)Co_0.8Fe_0.2O_3−δ powder has been successfully synthesized by a novel sol–gel thermolysis method using a unique combination of PVA and urea. The decomposition and crystallization behaviour of the gel precursor was studied by TG/DTA analysis. The gel precursor was calcined at different temperatures and the phase evoluation was studied by X-ray diffraction (XRD) analysis. From the result of X-ray diffraction patterns, it is found that a cubic perovskite (Ba_0.5Sr_0.5)Co_0.8Fe_0.2O_3−δ was formed by calcining the precursor at 450 °C for 5 h, but the well-crystalline cubic perovskite (Ba_0.5Sr_0.5)Co_0.8Fe_0.2O_3−δ was obtained by calcining the precursor at 650 °C for 5 h. Morphological analysis of the powder calcined at various temperatures was done by scanning electron microscope (SEM). Thermogravimetric (TG) results showed the lattice oxygen loss of the product was about ∼2% in its original weight in the temperature range 40–900 °C. Finally, thermal expansion and electrical conductivity of the synthesized material were measured by dilatometer and four-probe dc method, respectively.     

Magnesium borohydride as a hydrogen storage material: Properties and dehydrogenation pathway of unsolvated Mg(BH4)2

The decomposition of crystalline magnesium borohydride upon heating was studied using thermal desorption, calorimetry, in situ X-ray diffraction, and solid state NMR. Hydrogen release from Mg(BH₄)₂ occurs in at least four steps via formation of several polyborane intermediate species and includes an exothermic reaction yielding crystalline MgH₂ as an intermediate. The decomposition products may be only partially recharged after the very first step and also via hydrogenation of Mg metal. The intermediate formation of amorphous MgB₁₂H₁₂, was confirmed by ¹¹B NMR. A four-stage pathway for the thermal decomposition of Mg(BH₄)₂ is proposed.     

Structural and electrochemical characterization of xLi[Li1/3Mn2/3]O2·(1 − x)Li[Ni1/3Mn1/3Co1/3]O2 (0 ≤ x ≤ 0.9) as cathode materials for lithium ion batteries

A series of cathode materials with molecular notation of xLi[Li_1/3Mn_2/3]O₂·(1 − x)Li[Ni_1/3Mn_1/3Co_1/3]O₂ (0 ≤ x ≤ 0.9) were synthesized by combination of co-precipitation and solid state calcination method. The prepared materials were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques, and their electrochemical performances were investigated. The results showed that sample 0.6Li[Li_1/3Mn_2/3]O₂·0.4Li[Ni_1/3Mn_1/3Co_1/3]O₂ (x = 0.6) delivers the highest capacity and shows good capacity-retention, which delivers a capacity ∼250 mAh g⁻¹ between 2.0 and 4.8 V at 18 mA g⁻¹.