Double perovskite-type catalysts including La2CoMnO6 and La2CuMnO6 are first evaluated for the effectiveness in removing volatile organic compounds (VOCs), and single perovskites (LaCoO3, LaMnO3, and LaCuO3) are also tested for comparison. All perovskites are tested with the gas hourly space velocity (GHSV) of 30,000hr-1, and the temperature range of 100-600°C for C7H8 removal. Experimental results indicate that double perovskites have better activity if compared with single perovskites. Especially, toluene (C7H8) can be completely oxidized to CO2 at 300°C as La2CoMnO6 is applied. Characterization of catalysts indicates that double perovskites own unique surface properties and are of higher amounts of lattice oxygen, leading to higher activity. Additionally, apparent activation energy of 68kJ/mol is calculated using Mars-van Krevelen model for C7H8 oxidation with La2CoMnO6 as catalyst. For durability test, both La2CoMnO6 and La2CuMnO6 maintain high C7H8 removal efficiencies of 100% and 98%, respectively, at 300°C and 30,000hr-1, and they also show good resistance to CO2 (5%) and H2O(g) (5%) of the gas streams tested. For various VOCs including isopropyl alcohol (C3H8O), ethanal (C2H4O), and ethylene (C2H4) tested, as high as 100% efficiency could be achieved with double perovskite-type catalysts operated at 300-350°C, indicating that double perovskites are promising catalysts for VOCs removal.
Mesoporous Mn1.5Co1.5O₄ (MCO) spinel films were prepared directly on a conductive nickel (Ni) foam substrate via electrodeposition and an annealing treatment as supercapacitor electrodes. The electrodeposition time markedly influenced the surface morphological, textural, and supercapacitive properties of MCO/Ni electrodes. The (MCO/Ni)-15 min electrode (electrodeposition time: 15 min) exhibited the highest capacitance among three electrodes (electrodeposition times of 7.5, 15, and 30 min, respectively). Further, an asymmetric supercapacitor that utilizes (MCO/Ni)-15 min as a positive electrode, a plasma-treated activated carbon (PAC)/Ni electrode as a negative electrode, and carboxymethyl cellulose-lithium nitrate (LiNO₃) gel electrolyte (denoted as (PAC/Ni)//(MCO/Ni)-15 min) was fabricated. In a stable operation window of 2.0 V, the device exhibited an energy density of 27.6 Wh·kg-1 and a power density of 1.01 kW·kg-1 at 1 A·g-1. After 5000 cycles, the specific energy density retention and power density retention were 96% and 92%, respectively, demonstrating exceptional cycling stability. The good supercapacitive performance and excellent stability of the (PAC/Ni)//(MCO/Ni)-15 min device can be ascribed to the hierarchical structure and high surface area of the (MCO/Ni)-15 min electrode, which facilitate lithium ion intercalation and deintercalation at the electrode/electrolyte interface and mitigate volume change during long-term charge/discharge cycling.
Sequentially precipitated Mg-promoted nickel-silica catalysts with ageing performed under various ultrasonic intensities were employed to study the catalyst performance in the partial hydrogenation of sunflower oil. Results from various characterisation studies showed that increasing ultrasonic intensity caused a higher degree of hydroxycarbonate erosion and suppressed the formation of Ni silicates and silica support, which improved Ni dispersion, BET surface area and catalyst reducibility. Growth of silica clusters on the catalyst aggregates were observed in the absence of ultrasonication, which explained the higher silica and nickel silicate content on the outer surface of the catalyst particle. Application of ultrasound also altered the electron density of the Ni species, which led to higher activity and enhanced product selectivity for sonicated catalysts. The catalyst synthesised with ultrasonic intensity of 20.78 Wcm-2 achieved 22.6% increase in hydrogenation activity, along with 28.5% decrease in trans-C18:1 yield at IV = 70, thus supporting the feasibility of such technique.
Microbial fuel cell (MFC) is a promising technology that utilizes exoelectrogens cultivated in the form of biofilm to generate power from various types of sources supplied. A metal-reducing pathway is utilized by these organisms to transfer electrons obtained from the metabolism of substrate from anaerobic respiration extracellularly. A widely established model organism that is capable of extracellular electron transfer (EET) is Shewanella oneidensis. This review highlights the strategies used in the transformation of S. oneidensis and the recent development of MFC in terms of intervention through genetic modifications. S. oneidensis was genetically engineered for several aims including the study on the underlying mechanisms of EET, and the enhancement of power generation and wastewater treating potential when used in an MFC. Through engineering S. oneidensis, genes responsible for EET are identified and strategies on enhancing the EET efficiency are studied. Overexpressing genes related to EET to enhance biofilm formation, mediator biosynthesis, and respiration appears as one of the common approaches.
A highly mesoporous graphitic carbon nitride g-C3N4 (GCN) has been produced by a template-free method and effectively photodegrade tetracycline (TC) antibiotic under solar light irradiation. The mesoporous GCN (GCN-500) greatly improves the photoactivity (0.0247 min-1) by 2.13 times, as compared to that of bulk GCN (0.0116 min-1). The efficiently strengthened photoactivity is ascribed to the high porosity (117.05 m2/g), and improves the optical absorption under visible light (Eg = 2.65 eV) and good charge carrier separation efficiency. The synthesized mesoporous GCN shows a uniform pore size (~3 nm) distribution. GCN-500 shows large pore volume (0.210 cm3/g) compared to GCN-B (0.083 cm3/g). Besides, the GCN-500 also exhibits good recyclability and photostability for TC photodegradation. In conclusion, GCN-500 is a recyclable photocatalyst for the removal of TC under visible light irradiation.
A series of heteroatom-containing porous carbons with high surface area and hierarchical porosity were successfully prepared by hydrothermal, chemical activation, and carbonization processes from soybean residues. The initial concentration of soybean residues has a significant impact on the textural and surface functional properties of the obtained biomass-derived porous carbons (BDPCs). SRAC5 sample with a BET surface area of 1945 m2 g-1 and a wide micro/mesopore size distribution, nitrogen content of 3.8 at %, and oxygen content of 15.8 at % presents the best electrochemical performance, reaching 489 F g-1 at 1 A g-1 in 6 M LiNO3 aqueous solution. A solid-state symmetric supercapacitor (SSC) device delivers a specific capacitance of 123 F g-1 at 1 A g-1 and a high energy density of 68.2 Wh kg-1 at a power density of 1 kW kg-1 with a wide voltage window of 2.0 V and maintains good cycling stability of 89.9% capacitance retention at 2A g-1 (over 5000 cycles). The outstanding electrochemical performances are ascribed to the synergistic effects of the high specific surface area, appropriate pore distribution, favorable heteroatom functional groups, and suitable electrolyte, which facilitates electrical double-layer and pseudocapacitive mechanisms for power and energy storage, respectively.
Pharmaceutical residues are emerging pollutants in the aquatic environment and their removal by conventional wastewater treatment methods has proven to be ineffective. This research aimed to develop a three-dimensional reduced graphene oxide aerogel (rGOA) for the removal of diclofenac in aqueous solution. The preparation of rGOA involved facile self-assembly of graphene oxide under a reductive environment of L-ascorbic acid. Characterisation of rGOA was performed by Fourier transform infrared, scanning electron microscope, transmission electron microscopy, nitrogen adsorption-desorption, Raman spectroscopy and X-ray diffraction. The developed rGOA had a measured density of 20.39 ± 5.28 mg/cm3, specific surface area of 132.19 m2/g, cumulative pore volume of 0.5388 cm3/g and point of zero charge of 6.3. A study on the simultaneous interactions of independent factors by response surface methodology suggested dosage and initial concentration as the dominant parameters influencing the adsorption of diclofenac. The highest diclofenac adsorption capacity (596.71 mg/g) was achieved at the optimum conditions of 0.25 g/L dosage, 325 mg/L initial concentration, 200 rpm shaking speed and 30 °C temperature. The adsorption equilibrium data were best fitted to the Freundlich model with correlation coefficient (R2) varying from 0.9500 to 0.9802. The adsorption kinetic data were best correlated to the pseudo-first-order model with R2 ranging from 0.8467 to 0.9621. Thermodynamic analysis showed that the process was spontaneous (∆G = - 7.19 to - 0.48 kJ/mol) and exothermic (∆H = - 12.82 to - 2.17 kJ/mol). This research concluded that rGOA is a very promising adsorbent for the remediation of water polluted by diclofenac.
Oil and grease, carbohydrate, protein, and lignin are the main constituents of high strength wastewaters such as dairy wastewater, cheese whey wastewater, distillery wastewater, pulp and paper mill wastewater, and slaughterhouse wastewaters. These constituents have contributed to various operational problems faced by the high-rate anaerobic bioreactor (HRAB). During the hydrolysis stage of anaerobic digestion (AD), these constituents can be hydrolyzed. Since hydrolysis is known to be the rate-limiting step of AD, the overall AD can be enhanced by improving the hydrolysis stage. This can be done by introducing pretreatment that targets the degradation of these constituents. This review mainly focuses on the biological pretreatment on various high-strength wastewaters by using different types of enzymes namely lipase, amylase, protease, and ligninolytic enzymes which are responsible for catalyzing the degradation of oil and grease, carbohydrate, protein, and lignin respectively. This review provides a summary of enzymatic systems involved in enhancing the hydrolysis stage and consequently improve biogas production. The results show that the use of enzymes improves the biogas production in the range of 7 to 76%. Though these improvements are highly dependent on the operating conditions of pretreatment and the types of substrates. Therefore, the critical parameters that would affect the effectiveness of pretreatment are also discussed. This review paper will serve as a useful piece of information to those industries that face difficulties in treating their high-strength wastewaters for the appropriate process, equipment selection, and design of an anaerobic enzymatic system. However, more intensive studies on the optimum operating conditions of pretreatment in a larger-scale and synergistic effects between enzymes are necessary to make the enzymatic pretreatment economically feasible.
This work demonstrated the feasibility of an industrial-scale aerated static pile composting system for treating one of the common biowastes-soybean curd residue. The mixing ratios of the feedstock were optimized to achieve a carbon-nitrogen ratio and a moisture level in the ranges of 25-35 and 60-70%, respectively. This open-air composting system required 6-7 months to obtain a mature compost. Solvita and seed germination tests further confirmed the maturity of the compost, with 25% compost extract concentration yielding the best germination index in the absence of phytotoxicity. The bacterial and fungal compositions of the compost piles were further examined with metagenomic analysis. Thermoactinomyces spp., Oceanobacillus spp., and Kroppenstedtia spp. were among the unique bacteria found, and Diutina rugosa, Thermomyces dupontii, and Candida taylorii were among the unique fungi found in the compost piles, suggesting the presence of good microorganisms for degrading the organic biowastes.