Efficient treatment of organic pollutants by boron doped TiO2 photocatalysts under visible light radiation

As one of the most widely used photocatalysts, TiO2 suffers from the limited application with respect to harvesting solar energy for the environmental remediation. One way to perform the TiO2 modification is by doping, through which the doped TiO2 would be able to absorb the visible light from the solar illumination as a visible reactive catalyst. The objective of this work is to synthesize boron-doped TiO2 (B@TiO2) photocatalysts using a method called sol–gel. The as-synthesized catalysts were characterized using DR UV–vis spectroscopy, XRD, photoluminescence, XPS, SEM, EDS and TEM. The XRD results show that doping of boron constituent could hinder the grain crystallite growth and selectively favor the anatase phase formation and diboron trioxide phase, B2O3. The characterization works indicated an enhanced absorption edge of B@TiO2 and reduced band gap energy to enable the visible light photocatalytic activity. The lowest intensity of PL result signaled the slowest recombination rate of electron by supposedly newly created energy level by the doped boron, was achieved by 6B@TiO2. The 6B@TiO2 demonstrated the most efficient performance with greater than 93% of MB degradation, owing to the aforementioned modification of the optical and electronic properties during the optimization effort of catalyst synthesis. In this work, a less energy intensive sol–gel procedure was carried out to produce the equally efficient photocatalysts. As a conclusion, the doping mechanism has extended the absorption spectrum of TiO2 and successfully degraded the model dye within the controlled experimental conditions

Rice Husk Nanosilica Preparation and Its Potential Application as Nanofluids

The fast development in the extraction technique of silica from biomass has resulted in the signification use of silica in the industry. Rice is one of the world’s most significant plants, which serve as a carbohydrate intake for humans. Rice husk is one of the main agro-wastes comprising big quantities of silicate. This chapter presenting the review on rice husk nanosilica production techniques by thermal and chemical methods. A direction on efficient and sustainable nanosilica extraction method will be discussed. Apart from that, method on nanofluids preparation will be accumulated with respect to the end application. Moreover, the influence of nanoparticle in nanofluids in terms of heat conductivity, rheological properties, and stability will be discussed. The potential application area of silica nanofluids such as solar, automobile, electronic cooling, and biomedical application will be explored

Photoreforming hydrogen production by carbon doped exfoliated g-C3N4: Optimization using design expert®software

Carbon doping was ascertained as a best strategy to improve the surface area and electronic properties of g-C3N4. Additionally, the carbon material could extend the delocalization of pi-electrons consequently fostering the photocatalytic reactions. Herein, a newly formulated carbon doped exfoliated g-C3N4 was prepared by a facile hydrothermal technique. The photocatalytic experiments using formaldehyde aqueous solution was employed to examine the effect of time and catalyst dosage. Response surface methodology (RSM) was used to optimize the reaction parameters and determine the best operating conditions using Design Expert Software Version 7.1.6. The changes in the functional groups of the catalyst before and after the reaction was characterized by FTIR analysis. As a result, the characteristic peak of tri-s-triazine located at 802 cm−1 was present in the recycled catalyst. This outcome confirms that the melon structures were not destroyed after the reaction thereby revealing better stability of the catalyst. UV–Vis DRS analysis was used to evaluate the band gap of the as-prepared catalysts. From the one-factor-at-a-time (OFAT) results, the range of the independent variables were selected as follows: time (4–8 h) and catalyst dosage (0.5–1 g/L). Based on the central composite design (CCD) matrix, the optimum conditions for hydrogen yield (920 µmol/g) were observed at 6 h using 0.75 g/L of catalyst. In the optimization process, the response of the interactions between the parameters were given by the polynomial quadratic model and 3D plot. The influencing factors on the reaction were analysed by Analysis of Variance (ANOVA). The highest R-squared value of 0.9797 and F-value of 46.31 evidenced an excellent fitting of the model. Hence, this work provides some insights on the development of Carbon doped exfoliated g-C3N4 with their contribution towards photocatalytic field

Photoelectrochemical Performance of G-C3N4 for Hydrogen Production

Global energy crisis keeps arising and converting intermittent energies into storable chemical fuels, especially hydrogen is indeed a crucial obligation. Water splitting through photoelectrochemical (PEC) is certainly a promising technology intended for the current dilemma. Nevertheless, the broad applications of this system mainly depends on the exploration of efficient electrode materials. Accordingly, graphitic carbon nitride (g-C3N4) has high potentiality as a photoelectrode material for PEC water splitting. In the present work, g-C3N4 was fabricated by thermal polycondensation technique and characterised by numerous analysis techniques, including XRD, FTIR, UV-Vis and Mott-Schottky. The hydrogen evolution was deliberated by electrochemical analysis in the three-electrode PEC system. LSV analysis revealed that during the light irradiation, the current generated was higher (0.45 mA/cm2), whereby the current density represents the amount of hydrogen gas evolved

Conversion of Food Processing Waste to Bioenergy: Bangladesh Perspective

Microbial fuel cell (MFC) is an attractive renewable and sustainable technology to meet up the drastic energy crisis of the world through waste water treatment. This Bioelectrochemical system (BES) converts biomass spontaneously into electricity by the metabolic activity of microorganisms. Food processing industry generally discharges large volume of wastewater, which creates adverse financial and ecological impacts to the industry and environment. In this present contribution, electricity production from food processing industry wastewater that serves as substrates in MFCs was investigated. Dual chambered mediator-less MFC was designed and fabricated using locally available materials. Performance of the MFC was evaluated by measuring potential parameters, such as current generation, current density, change in pH, and change in chemical oxygen demand at different operating conditions. Polarization experiments were conducted to find the maximum power density. Current generation increased with increasing sludge loading, and maximum results were recorded as 90 µA with 9 g of sludge and optimum pH value 8 in the anode chamber. This study documented a maximum power density of 7.42 mW/m2 with the corresponding current density of 25 mA/m2. Citation: Amin, M. S. A., Talukder, M. J., Raju, R. R., and Khan, M. M. R. (2019). Conversion of Food Processing Waste to Bioenergy: Bangladesh Perspective. Trends in Renewable Energy, 5(1), 1-11. DOI: 10.17737/tre.2019.5.1.008

A kinetic model for the photocatalytic reduction of CO2 to methanol pathways

Carbon dioxide (CO2) is one of the greenhouse gases that contribute to global warming. CO2 could be converted to valuable products such as hydrocarbons through the photocatalytic process. The aim of this research was to develop the kinetic model for the photocatalytic reduction of CO2 to methanol (CH3OH) in liquid phase reaction using cerium oxide-titanium dioxide (CeO2-TiO2) catalyst. The Langmuir-Hinshelwood approach was used in developing rate laws for the catalytic reaction using the catalytic reaction mechanism proposed. The catalytic reaction mechanism is about the adsorption of reactant (CO2 dissolved in the liquid phase), the reaction on catalyst surface and desorption of product. The experimental kinetic data were evaluated in the Polymath 6.1 software. In this study, two types of mechanism are proposed whereas one is considered the carbon monoxide (CO) oxidation while the other is not. Based on the model fitting, it was found that the model considers the CO oxidation is fitted well with the experimental data represents that the oxidation reaction of intermediate product, CO is the rate-determining step in the photocatalytic reduction of CO2 to CH3OH in liquid phase reaction

Highly effective B@g-C3N4/polyaniline nanoblend for photoelectrocatalytic reduction of CO2 to methanol

Photoelectrocatalytic (PEC) conversion of CO2 has been extensively investigated as it uses solar energy to combine CO2 and water to produce hydrocarbons. In the present work, B@graphitic carbon nitride (g-C3N4)/polyaniline (PANI) nanoblend was synthesized by in situ polymerization of aniline in the presence of B@g-C3N4 for PEC CO2 reduction. The catalyst was characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy, X-ray diffraction, UV-Vis absorption spectroscopy, photoluminescence, X-ray photoelectron spectroscopy (XPS), and Mott-Schottky analysis. The PEC activity was evaluated by linear sweep voltammetry (LSV) and chronoamperometry. XRD revealed the formation of g-C3N4, while B doping was confirmed by XPS. The presence of PANI was visualized by FESEM. A remarkable cathodic current associated with CO2 reduction was observed during LSV from an onset potential of –0.01 V vs. normal hydrogen electrode (NHE), which is more positive than that of B@g-C3N4 (–0.82 V vs. NHE), and the positive shift is attributed to the slow charge recombination kinetics of B@g-C3N4/PANI as evidenced by PL results. The mechanism of PEC CO2 reduction was investigated and discussed on the basis of the Mott-Schottky results. In conclusion, B@g-C3N4/PANI opens a new avenue to develop photoelectrocatalysts for PEC CO2 reduction to methanol

Electrochemical Study of Copper Ferrite as a Catalyst for CO2 Photoelectrochemical Reduction

In this work, p-type CuFe2O4 was synthesized by sol gel method. The prepared CuFe2O4 was used as photocathode catalyst for photoelectrochemical (PEC) CO2 reduction. The XRD, UV-Visible Spectroscopy (UV-Vis), and Mott-Schottky (MS) experiments were done to characterize the catalyst. Linear sweep voltammetry (LSV) was employed to evaluate the visible light (λ>400 nm) effect of this catalyst for CO2 reduction.  The band gap energy of the catalyst was calculated from the UV-Vis and was found 1.30 eV. Flat band potential of the prepared CuFe2O4 was also calculated and found 0.27 V versus Ag/AgCl. Under light irradiation in the CO2-saturated NaHCO3 solution, a remarkable current development associated with CO2 reduction was found during LSV for the prepared electrode from onset potential -0.89 V with a peak current emerged at -1.01 V (vs Ag/AgCl) representing the occurrence of CO2 reduction reaction. In addition, the mechanism of PEC was proposed for the photocathode where the necessity of a bias potential in the range of 0.27 to ~ -1.0 V vs Ag/AgCl was identified which could effectively inhibit the electron-hole (e-/h+) recombination process leading to an enhancement of CO2 reduction reactions.

Significant improvement of power generation through effective substrate-inoculum interaction mechanism in microbial fuel cell

Low power generation and low voltage output is a common problem in microbial fuel cell (MFC) run with complex wastewater. Biocatalysts are one of the major components to ensure the high performance of the MFCs. In the present study, palm oil mill effluent (POME) is treated with a combination of Saccharomyces cerevisiae, Klebsiella variicola and Pseudomonas aeruginosa to intensify the power generation and treatment efficiency of the MFC. MFCs are catalyzed by pure cultures exhibited low power generation in the range of 50–103 mW/m2 whereas the yeast-bacteria inoculum demonstrates 5–10 fold higher power generation (500 mW/m2 at 0.67 V) with ~90% COD removal efficiency. The mechanism of enhanced power generation by yeast-bacteria inoculum is unravelled which suggests that Klebsiella variicola and Pseudomonas aeruginosa play a crucial role in transferring the electrons from the bulk phase to the electrode surface through self-produced electron-shuttles and at the same time extract electrons from the yeast leading to high power generation. Moreover, substrate-inoculum synergism also offers higher wastewater treatment efficiency. The findings of the work suggest that the use of substrate-inoculum mutualistic interaction between yeast and bacteria as a profound replacement to the existing bacterial inoculum for achieving higher performance in MFCs

Potentiality of petrochemical wastewater as substrate in microbial fuel cell

The petrochemical wastewater (PCW) from acrylic acid plant possesses very high chemical oxygen demand (COD) due to presence of acrylic acid along with other organic acids. The treatment of PCW by conventional methods is energy intensive. The treatment of PCW with concurrent power generation by employing microbial fuel cell (MFC) could be a potential alternative solving the problem of energy and environment. The goal of the present paper is to evaluate the viability of treating the wastewater using anaerobic sludge as biocatalyst in a dual- chamber MFC for simultaneous power generation and wastewater treatment. This study demonstrates that anaerobic sludge (AS) could work as a biocatalyst producing maximum power density of 0.75 W/m3at current density and open circuit voltage (OCV) of 412 mA/m2 and 0.45 V respectively using PCW with an initial COD of 45,000 mg/L. The COD removal efficiency and the columbic efficiency (CE) were found 40% and 13.11%, respectively. The mechanism of electron transfer in the anode was analyzed by cyclic voltammetry (CV) and the resistances across the electrode/biofilm/solution interface were investigated by employing impedance spectroscopy (EIS). The current work proves the capability of the MFC for the treatment of acrylic acid plant PCW using anaerobic sludge (AS) as biocatalyst