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Sugar beet pulp (SBP) is a major byproduct from the sugar industries and consists of >20% w/w arabinose. The current work evaluated the potential of Enterobacter ludwigii assimilating pure arabinose and arabinose rich hydrolysate from SBP pellets for 2,3-butanediol (BDO) production. The hydrolysate was obtained through dilute acid pretreatment (DAP) with sulphuric acid. The process was optimized for acid and solid loading to obtain a hydrolysate free from furan derivatives. The effect of different levels of substrate (10–60 g/L) using pure arabinose was conducted in shake flask experiments, followed by co-fermentation with small amounts of glucose and SBP hydrolysate. After flask cultivations, BDO fermentations were carried-out in a bench-top bioreactor in batch and fed-batch modes using pure arabinose as well as SBP hydrolysate. The fed-batch culture led to BDO production of 42.9 and 35.5 g/L from pure arabinose and SBP hydrolysate with conversion yields of 0.31 and 0.29 g/g, respectively. Finally, BDO accumulated on pure arabinose and SBP hydrolysate were recovered using an aqueous two-phase extraction system. The recovery yield of BDO accumulated on arabinose and hydrolysate was ∼97%. The work demonstrated the feasibility of using SBP as a suitable feedstock for manufacturing BDO.

Lignin is one of the most abundant naturally occurring polymers and can produce value-added products such as vanillin and p-coumaric acid. In the current work, in-situ depolymerization of lignin for its valorization in a microbial peroxide-producing cell (MPPC) system was performed. It is an electrochemical cell that requires no external energy to produce H

Nitrogen-functionalized graphene oxide (GO) nanocatalysts were prepared using ammonia, methylamine, ethylamine, and hydrazine hydrate as a nitrogen source. Nanocatalysts samples were thoroughly characterized using XRD, Raman, FTIR, XPS, FESEM, TEM, and TGA techniques. Quantitative and qualitative analyses of surface acidic and basic sites were done by NH3- and CO2-TPD techniques. Nanocatalysts were further examined for DMC production via transesterification reaction of propylene carbonate (PC) with CH3OH. Quantitative analysis of nitrogen-containing functional groups in the prepared sample with respect to other functional moieties was performed. Among various nanocatalysts, ammonia functionalized GO (AGO) was found to be the best for DMC production. At optimized reaction conditions of temperature (180 °C), time (6 h), and catalyst dose (1 wt% with respect PC), the highest DMC yield of ∼50% was observed. Reusability studies using AGO nanocatalyst were conducted up to four consecutive test cycles to evaluate catalysts' potentiality towards DMC synthesis. Thus, N-functionalized GO is a useful metal-free nanocatalyst that could also be explored for other chemical processes.

This study reports an electrochemical reduction of the NO3− along with oxidation of the in-situ generated NH4+ with maximum selectivity of the N2 gas as the final-product. The use of aluminum as a cathode and Ti/RuO2 as an anode showed enhanced electrochemical nitrate reduction at the cathode and oxidation of the ammonium ion at the anode. Effects of various parameters like initial NO3− concentration (Co = 100−400 mg L−1), a dose of the Cl− as NaCl (NaCl = 100−400 mg L−1), current density applied (j = 83.3-333.3 A m−2), solution pH (pH = 4–10) and electrolysis time (t = 0−120 min) were studied in terms of NO3− reduction and total nitrogen (TN) removal efficiencies. Current efficiency (CE) was elaborated with respect to end products like N2, NO2− and NH4+. Specific electrical energy consumption (SEC) was calculated in kWh kg−1 NO3− removed for the electrochemical process. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were utilized for understanding the oxidation/reduction mechanism over electrodes and the characteristics of the electrodes in a different solution. The studied mechanism suggested a circular conversion of NO3− through complex processes into the N2 gas as the final product. The ultimate nitrate and TN degradation efficiency of ≈95 % with N2 selectivity of ≈100 % were achieved at the optimum condition of Co = 100 mg L−1, NaCl = 300 mg L−1, j = 333.3 A m−2, pH = 6 and time = 120 min with SEC = 927.4 kW h kg−1 NO3− removed. The 1st, 2nd, and nth-order kinetic models were used for the reaction kinetics. FE-SEM, XRD, and AFM techniques were used for the characterization of the electrodes before and after all the electrochemical runs. The operating cost was calculated for lab-scale treatment along with a comparison with previous studies. No sludge or scum got produced for each electrochemical run. Finally, this study delivers a superior perceptive for electrochemical characteristics of Al at the cathode side and Ti/RuO2 at anode side as well as electrochemical NO3− reduction and oxidation of the generated NH4+, simultaneously.

Present study proposed a sorption and desorption approach of aqueous mercury ion (Hg2+) on sulfur impregnated attapulgite (ATPS) adsorbent. Morphological characterization of natural and impregnated ATP confirmed the mesoporous nature of ATPS-adsorbents. The presence of various types of functional groups on the surface of ATPS was confirmed by using the zeta-potential measurement, X-ray fluorescence (XRF), and FT-IR analysis. Batch adsorption tests were carried out to detect the optimum condition of temperature for sulfur impregnation, and the results illustrated that the best adsorbent (ATPS-500) produced via the impregnation at 500 °C, with the highest equilibrium uptake of Hg2+ at initial pH 7. Different parameters like solution pHo, initial concentration of mercury (Co), temperature (T), contact time (t) and the effect of co-existing ions were optimized. Optimum pH and equilibrium contact time at the optimum dose of adsorbent (m) = 0.02 g in 50 mL and Co = 2.0 mg L − 1 were found to be pH~5 and 24 h at T = 313 K for ATPS-500.The best representation of adsorption kinetic was followed by the pseudo-first order kinetic model. The adsorption of Hg2+ions onto ATPS-500 was found to be endothermic. The heat of adsorption and changes in the entropy of Hg2+ions sorption on ATPS-500 were determined as 10.35 kJ mol−1 and 0.16 kJ mol−1 K − 1, respectively. Thermal regeneration represented that ATPS-500 was used for five desorption–sorption cycles with excellent efficiency of Hg2+ in each cycle.

Perfluorooctanoic acid (PFOA) is a chemical used for both commercial and industrial applications. It has turned out to be worldwide anxiety owing to its extensive existence in the water bodies and subsequent harmful ecological effects. This study illustrates the significance of hybrid aerated electrocoagulation (EC) and modified peroxi-coagulation (PC) for the PFOA degradation in an aqueous solution. Consumable iron plate electrodes were employed as an electrode pair in both EC and modified PC processes. The laboratory tests were conducted in a batch reactor with a functioning capacity of 1 L. Aeration improved the EC process performance considerably. Higher than 56% PFOA and 38% defluorination occurred after 60 min of electrolysis with EC being operated at a pH of 3.6 and applied a current density of 78.34 Am−2. The performance of the modified PC process was considerably higher than that of the aerated EC process. More than 90% PFOA, 87%total organic carbon (TOC), and 71% deflorination were attained with modified PC process after 60 min of electrolysis operated at 78.34 Am−2 and initial pH of 3.6 when 50 mM hydrogen peroxide (H2O2) was added. The superior performance of the modified PC than aerated EC is mostly owing to the attack of in-site produced OH• radicals. PFOA decayed stepwise into small‒chain perfluoro carboxylic acids (PFCAs) and fluoride ions during modified PC oxidation.

The present study investigated the roles of peroxydisulfate (PDS) radicals and sulfate radicals (SO

In this study, zinc ferrocyanide nano-composite materials were synthesized and developed by reaction of aqueous K4Fe(CN)6·3H2O and ZnCl2 in the presence of tri-block copolymer and tert-butanol. The synthesized catalysts were characterized by CO2- and NH3-temperature-programmed desorption (TPD), N2-sorption, SEM, TEM, XRD and used for transesterification reactions. The zinc ferrocyanide catalyst showed a sharp cube shaped structure with a high amount of basic sites. The zinc ferrocyanide catalyst showed type IV isotherm with H3 hysteresis loop. BET surface area and pore volume were found to be 125 m2/g and 0.1395 cm3/g, respectively. The transesterification of Jatropha oil using Fe-Zn-1 showed the maximum 94.5% jatropha oil conversion. The prepared catalyst can be easily recovered and successfully reused after five times. The slight loss of activity of Fe-Zn-1 catalyst can be attributed to the deposition of the reaction products on the active sites and the blockage of the pores. Overall, the zinc ferrocyanide catalyst activity was found to be directly dependent upon both the textural and surface basic/acidic properties.

In the present work, a detailed thermo-kinetics of hazardous sulfur-rich sludge generated from the corn processing industry was performed for acquiring the optimum parameters for the efficient recovery of sulfur using the evaporation-condensation technique. Sulfur in the sludge was found to be 79 ± 3% (wt%) as estimated by the Bureau of Indian Standards method. A weight loss of 77 ± 3% was found in the active devolatilization zone from ≈ 200–400 °C. The online FTIR confirmed the evolution of mainly sulfur vapors (S8) along with some sulfur dioxide (SO2) and disulfur (S2). The thermogravimetric data (TG) was used to evaluate the kinetic parameters with the help of model-free methods, and Z-master plots determined additional insight into the reaction mechanism. Furthermore, the calculated activation energy (Ea) was used to determine the thermodynamic feasibility. The average Ea values appraised by FM, FWO, sDAEM, and ST models were 55.43, 72.04, 62.33, and 62.67 kJ mol−1, respectively. Overall, 91.2% of sulfur was successfully recovered at 400 °C, having 99 ± 0.5% purity. The approximate cost analysis of the sulfur recovery process was also estimated to check the economic viability. Recovered sulfur could be directly used for industrial and agricultural applications without any further purification.

Two kinetic models, i.e., schemes, surface adsorbed nitrogen as divergent (SND) and surface adsorbed NO as divergent (SNOD) towards NH4+ and N2 production, were developed to model simultaneous electrochemical reduction of the nitrate ion (NO3−) and oxidation of by-products. Experimental data for electrochemical reduction was collected in synthetic nitrate solution and actual wastewater using Al and Ti/RuO2 as cathode and anode, respectively. Sum of square errors (SSE) and Akaike's information criterion (AIC) analysis showed that the SND model well-represented all the concentration profiles of nitrogen species with the variation in all the operating parameters. Desorption of nitrite ion from the cathode surface was the rate-determining step for the SND kinetic model. Mechanistic and kinetic analysis suggested that N2 gas was the main product. However, NO2− gets formed as the by-product in the alkaline environment, whereas, NO2− and NH4+ were the by-products in the acidic environment.

This study reports the calculation of individual ion's activity coefficient and total minimum Gibbs energy for electrochemical denitrification of nitrate ions in synthetic and actual wastewater. The concentration of nitrate ion continuously decreased during treatment via the electrochemical method. During the treatment, nitrate ions got reduced into nitrite and ammonium ion. The individual ion activity coefficient was examined by applying Pitzer, Lin and Lee modified Debye-Huckel theory which is based on the interaction of ion-ion (long-range, i.e., LR interaction-electrostatic effect) and ion-water (short-range, i.e., SR interaction-solvation effect) in the aqueous solution. The equilibrium composition of these ions was calculated by minimizing the error between total minimum Gibbs energy calculated by using experimental and predicted compositions. The individual ion activity coefficient, which was calculated through this model, was used to measure the total minimum Gibbs energy (Gtotal). Variation of individual ion activity coefficient and Gtotal with initial nitrate ion concentration, applied current density, initial pH, and concentration of NaCl as electrolyte has been studied. It was found that the experimental and calculated composition of nitrate, nitrite, and ammonium ions were in good agreement for electrochemical denitrification of synthetic and actual wastewater.

This study aims to investigate the mineralization of cosmetics producing industrial wastewater (CW) using sono-electrochemical (US-EC) treatments. The influence of operating parameters such as current density (j), electrolyte (Na2SO4) concentration (m), initial pH (pHo), and ultrasonic power was investigated using Ti/RuO2 dimensionally stable electrodes. The results demonstrated 80.9% chemical oxygen demand (COD) removal efficiency, 433.5 kWh (kg COD removed)−1 of specific energy consumption at the optimum conditions of P = 100 W, j = 213 A m−2, pHo= 7.6 (natural pH), and m = 1.5 g L−1. With the application of ultrasound, COD removal efficiency increases from 60.2% to 80.9%, with a synergistic effect of 1.1. Kinetics study analysis confirms that mineralization follows the nth order kinetics model. In the presence of ultrasound, the performance of electrochemical treatment gets enhanced due to higher electron transfer, the enhanced production of •OH radicals, and sulfate radicals (SO4•−). The pathway for the degradation of the compound was suggested by quadrupole time of flight mass spectroscopy (QToF-MS). The operating cost of the process was also evaluated to establish the applicability of the US-EC process at the industrial scale.

The need for eco-friendly fuels has given a fillip to search for new molecules and their cost-effective synthesis. A series of ceria-strontium (CexSr1−xO2; x = 0 to 1) catalysts were prepared by a citric acid assisted sol–gel method. These catalysts were characterized by BET, XRD, SEM-EDAX, ICP-MS, FTIR, NH3-TPD and CO2-TPD techniques and tested for the synthesis of dimethyl carbonate (DMC) in a batch reactor for the transesterification of ethylene carbonate (EC). The activity of the synthesized catalysts was found to be closely related to basic and acidic sites, and the surface area of the catalysts. The catalyst, Ce0.6Sr0.4, showed highest basicity and acidity, and was found to be most effective in the formation of DMC from transesterification of EC. Reactions were carried out by varying the particle size (50–800 μm) and agitation speed (200–600 rpm) for minimizing the internal mass transfer resistance and the external mass transfer resistance, respectively. Further, Ce0.6Sr0.4 catalyst was used to optimize the reaction conditions such as methanol/EC molar ratio (in the range of 4–12), catalyst dose (in the range of 2–5 wt% of EC), reaction time (in the range of 2–6 h) and temperature (in the range of 100–180 °C) for DMC yield and EC conversion. At the optimum conditions of methanol/EC molar ratio of 8, 3 wt% of catalyst, 5 h reaction time and 150 °C temperature, the DMC selectivity was 87% and EC conversion of 82%, with a reaction rate of ∼0.547 mol/L.h (with respect to EC). The reusability of the Ce0.6Sr0.4 catalyst for EC conversion with turn-over frequency and DMC selectivity were also studied.

A highly efficient G/La heterogeneous catalyst comprising of reduced graphene oxide (rGO) and lanthanum oxide (La2O3) was developed using the in-situ hydrothermal technique. Four different catalyst samples with graphene content of 0.2, 0.5, 1.0, and 2.0 were prepared and tested against dimethyl carbonate synthesis (DMC) synthesis using the transesterification method. Structural analysis by scanning electron microscopy revealed that La2O3 displayed nanorod morphology. DMC synthesis results showed that G/La-3 composite with 1% graphene content outperformed others and showed the highest DMC yield of ~84% at 180 oC. The excellent performance of G/La-3 was attributed to the synergistic effect of 2-D rGO and 1-D La2O3 nanorods, which showed the highest surface area of 76.54 m2/g. Moreover, the existence of acidic and basic active sites as identified by the temperature-programmed desorption (TPD) technique facilitates DMC production over the surface of G/La-3 catalyst. Recyclability and reusability experiments showed a gradual decrease in DMC yield owing to catalyst deactivation. It is expected that the present work provides valuable visions of the applicability of graphene/rare earth metal oxide heterogeneous catalysts in the given or similar chemical transformation processes.

This paper reports the use of novel ceria-zinc catalyst for the preparation of dimethyl carbonate (DMC) using transesterification of PC with methanol. Ceria-zinc oxide catalysts were prepared by a sol-gel method using citric acid, oxalic acid and tartaric acid as chelating agents (named as CZC, CZO, and CZT, respectively). The synthesized catalysts were characterized by XRD, N2 adsorption-desorption, FTIR, SEM-EDX, ICP-OES, and CO2-temperature program desorption. Experimental results revealed that the catalytic performance of CZC was closely related to the surface area and presence of basic sites in the catalyst. CZC showed high selectivity and PC conversion. Effects of operating parameters such as methanol/PC molar ratio, catalyst dose, reaction temperature, reaction time were studied. The reusability of CZC as a catalyst for DMC selectivity and PC conversion with turn-over frequency (TOF) was also studied.

Biosilica was synthesised via thermal method from teff ( Eragrostis tef ) straw, an African agricultural waste, at three different ashing temperatures. Raw teff, characterised by various method, was subjected to thermal decomposition in static air in an electric muffle furnace at various temperatures for 2 h. X-ray fluorescence (XRF) characterization technique analysis showed thermally treated teff straw ash contains significant amount of biosilica having purity of 85, 91.2 and 91.8% for samples obtained at ashing temperatures of 500 °C, 700 °C, and 900 °C, respectively. Teff straw biosilica samples were also characterised by various sophisticated techniques: FE-SEM/EDX, FTIR), XRD and TEM. Prepared biosilica samples performed well for adsorptive removal of pyridine from aqueous solution. Present experimental results show that teff straw is highly-potent renewable source for biosilica when compared with other materials reported in the literature under similar conditions.

Highly acidic (pH

This study focuses on the "green" conversion of glycerol to 1,2-propanediol using the Cu-Al-Zn catalyst prepared by the co-precipitation method. Different ratios of (Cu+Zn)/Al were synthesized; the Zn and Al contents were varied while the Cu was kept constant (the Zn/Al ratios were 3:1, 4:1, 5:1, and 6:1). Catalyst characterization using TPD, XRD, and SEM, showed that the synthesized catalysts consisted of hydrotalcite with basic and acidic sites. The basicity of the catalysts was found to be an important criterion for the catalytic transfer hydrogenation, with the basic sites of the catalyst increasing the conversion of glycerol. Copper appeared to have an impressive effect on the C-O/C-C cleavage of glycerol during indirect hydrogenolysis for the synthesis of 1,2-propanediol. A reaction mechanism based on the hydrogenation of ethanol at Cu sites and the formation of intermediates at the basic sites of the catalysts was proposed.

Diethyl carbonate (DEC) is a linear organic carbonate which has applications as a fuel additive, in production of polycarbonates, and as a solvent in lithium ion batteries. Ethanolysis of urea, as compared to other methods of DEC synthesis, has an edge having requirements of cheap and abundant raw materials. However, only few studies have been reported due to low acidity of ethanol. In the present study, cerium-zinc based oxides in various molar ratios were used for DEC synthesis from ethanol and urea. These catalysts were prepared by auto combustion technique and characterized by thermogravimetric analysis (TGA), Raman spectroscopy, X-ray diffraction (XRD), N 2 adsorption-desorption, field emission scanning electron microscope (FE-SEM), energy dispersive X-ray (EDX), Fourier transform infra-red (FTIR), and NH 3 - and CO 2 -temperature programmed desorption (TPD) methods. No additional phases except pure Ce and Zn oxide were observed in the catalyst from XRD analysis. Effects of pore surface area and surface acidity/basicity were found to be profound in the synthesis of DEC. DEC yield of 28.8% was obtained at 190 °C and 5 h using Ce 0.1 -Zn 0.9 mixed oxide. Effect of operating parameters such as ethanol/urea molar ratio, temperature, time and catalyst concentration were also studied.

In this study, ceria-zirconia based catalysts (CeO 2 , ZrO 2 and Ce 0.5 Zr 0.5 O 2 ) were synthesized by hydrothermal method and characterized by N 2 -sorption, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Acidity and basicity of synthesized catalysts were investigated by NH 3 and CO 2 temperature-programmed desorption (TPD). Brunauer-Emmett-Teller (BET) surface area of CeO 2 , Ce 0.5 Zr 0.5 O 2 and ZrO 2 were found to be 88, 117 and 70 m 2 g −1 and average crystallite sizes was 9.48, 7.09 and 9.45 nm, respectively. These catalysts were further used for direct conversion of CO 2 with methanol for the synthesis of dimethyl carbonate (DMC). DMC yield was found to be highly dependent upon the both basicity and acidity of catalysts. Ce 0.5 Zr 0.5 O 2 catalysts showed better activity as compared to CeO 2 and ZrO 2 catalysts. Effect of reaction conditions (such as catalyst dose, reaction temperature and reaction time) and catalyst reusability was studied with Ce 0.5 Zr 0.5 O 2 catalyst. The optimum operating condition for direct conversion of CO 2 into DMC at constant pressure of 150 bar were found to be reaction time = 24 h, catalyst dose = 1.25 g and temperature = 120 °C. Moreover, chemical equilibrium modeling was performed using Peng–Robinson–Stryjek–Vera equation of state (PRSV-EoS) along with the van der Waals one-fluid (1PVDW) mixing rule to calculate the heat of reaction and Gibbs free energy change.

Carbon dioxide has generated great interest in recent years because of its potential usage as an alternative to traditional sources of carbon such as natural gas, petroleum and coal. In this paper, CO2 in combination with methanol was used for dimethyl carbonate (DMC) synthesis in presence of cerium-calcium mixed oxide catalysts. Catalysts with different Ce/Ca molar ratios were synthesized using surfactant templating method and characterized by powder X-ray diffraction (XRD), Raman spectroscopy, N2–sorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and temperature-programmed desorption (TPD) of CO2 and NH3. The direct conversion of CO2 was found to be highly dependent upon the acidity and basicity of catalysts. Brunauer-Emmett-Teller (BET) surface area of Ce3 Ca1, Ce1 Ca1 and Ce1 Ca3 was found to be 102, 82, 109 m2/g, respectively, and the average pore diameter was 9, 12 and 5 nm, respectively. The Ce1 Ca1 catalyst performed the best due to its combined acidic-basic properties. In addition, the catalyst was reused up to five cycles without significant loss of performance.

In this work, we report a strategy for synthesizing morphology-controlled hierarchical self-assembled, three dimensional (3D) porous wool ball (W-ball) like zinc oxides (ZnO) with excellent catalytic performance. A precursor, hydrozincite (Zn 5 (CO 3 ) 2 (OH) 6 ), was first synthesized via a green urea-glycerol assisted template-free hydrothermal approach, which was calcined to form crystalline 3D porous ZnO having nanostructured morphology. The effect of synthesis process parameters which control the morphology of ZnO were studied. ZnO was found to possess tunable pore characteristics with comparatively high specific surface area of 68 m 2 g −1 , and excellent acid-base surface properties. Prepared catalysts exhibited excellent photocatalytic performance for the treatment of highly toxic rhodamine B (RhB) dye under UV radiation. Zeta (ζ)-potential and dye adsorption tests were performed. Reusability experiments showed that after five cycles, catalysts exhibited 87% removal efficiency without any noticeable loss of the activity.

Electrochemical method has been utilized to synthesize zinc-copper nanocomposite using aqueous succinic acid as electrolyte solution. Both copper and zinc electrodes were used as anodes, kept on each side of cathode, which itself was made of zinc. Synthesized nanoparticles were characterized by scanning electron micrograph (SEM), point energy dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy, UV–visible diffuse reflectance spectroscopy (UV-DRS) and X-ray diffraction (XRD) analysis so as to determine its various physico-chemical characteristics. XRD analysis showed the incorporation of pure monoclinic copper oxide within hexagonal zinc oxide within ZnO/CuO which was further reaffirmed by point EDX analysis. EDX spectrum confirmed the presence of Cu, Zn and O elements in nanocomposite. SEM micrograph indicates that the obtained ZnO/CuO nanocomposite was in spherical morphology. Optical properties investigated by UV-DRS showed decrease in maximum reflectance (~22%) due to incorporation of CuO within ZnO nanoparticle. The electrochemical response of ZnO/CuO reveals higher electrochemical activity than pure ZnO, without any modification.

Electrochemical oxidation of 4-chlorophenol (CP) was investigated (in terms of chemical oxygen demand (COD) and CP removal efficiencies) by using a dimensionally stable anode (DSA) namely ruthenium oxide coated titanium (Ti/RuO 2 ) electrode. Effect of process conditions such as current density ( j ), electrolyte concentration ( m ), initial pH (pH o ), time ( t ) and initial CP concentration ( C o ) has been studied. Current efficiency (CE) and specific energy consumption (SEC) were also measured. Gas chromatograph-mass spectrometry (GC/MS) analysis was used to understand the CP mineralization mechanism which has been established on the basis of intermediates identified such as benzoquinone, hydroquinone and organic acids. Reaction kinetics was expressed by pseudo-first order kinetic model. Maximum COD removal efficiency of 96.7% and CP removal efficiency of 97.2%, respectively, was observed at j = 222.22 A/m 2 , t = 180 min, pH o = 5.2 and m = 400 mg/l with SEC = 655 kWh/kg COD. Operating cost based on the studies performed on laboratory scale EC reactor has been calculated and compared with those reported for other pollutants degradation.

Present study demonstrates reutilization of electrochemical (EC) sludge as a potential low-cost green catalyst for dye degradation. Hexagonal Fe2O3 type phase with trevorite (NiFe2O4)-type cubic phase nanocomposite material (NCM) was synthesized from solid waste sludge generated during EC treatment of textile industry wastewater with stainless steel electrode. For NCM synthesis, sludge was heated at different temperatures under controlled condition. Various synthesized NCMs were characterized by powder X-ray diffraction (PXD), energy dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis. The synthesized NCMs were found to contain iron, chromium, nickel and oxygen in the form of α-Fe2O3 (metal: oxygen = 40:60), (Fe,Cr,Ni)2O3 and trevorite NiFe2O4, (Ni,Fe,Cr) (Fe,Cr,Ni)2O4 (metal: oxygen = 43:57). Field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), pore size distribution, and atomic force microscope (AFM) analysis showed distribution of grains of different shapes and sizes. Catalytic activity of NCM was studied by the methylene red dye degradation by using the catalytic wet peroxidation process. Zeta potential study was performed under different pH so as to determine the performance of the NCMs during dye degradation.

Persistent organic pollutants (POPs), which are highly toxic and potential health hazards, are discharged in wastewater and cannot be mineralized by conventional biological and physicochemical methods of wastewater treatment. Advanced oxidation processes (AOPs) such as electrochemical, sonochemical, photolysis, Fenton, and Fenton like processes seem to be good and promising wastewater treatment technology alternatives. However, flaws limit their use in industrial applications. Recently, combined AOPs have gained attention among researchers to overcome these flaws of single AOPs. In this review, we studied the combined sonolysis and photolysis techniques for the degradation of the POPs. The efficiency of sono-photolysis has been examined by considering the single strategies, i.e., sonolysis and photolysis process, and the effect of various parameters of sono-photoreactor on the kinetics of degradation. Combined irradiation of ultrasound and ultraviolet light has been reported to give the synergistic effect under different mechanisms. The physical feature of ultrasound provides the intense mixing of the pollutant, which supports UV light to deeply penetrate the medium and accelerate the hydroxylation/oxidation reaction where toxic pollutants generated due to photolysis were degraded. H2O2 generated during the transient collapse of microbubble experienced a photocleavage to produce additional •OH radicals, which increases the degradation of the pollutants. A significant synergistic effect has been reported during combined treatment due to the increase in •OH radicals generation and photolysis of H2O2 either added externally or formed by the US, which also avoids the secondary pollution. Critical analysis of the geometry of various types (batch and continuous) of the sono-photo reactor used during treatment have also been evaluated. The kinetics of the degradation process has been reviewed in detail. This review article demonstrates a thorough and critical analysis (1998–2020) of sono-photolysis techniques, which improve the understanding of combined treatment and provides an outline direction for future research.

The removal of phenol (P), 4-chlorophenol (CP), 4-nitrophenol (NP), catechol (C), resorcinol (R) and hydroquinone (HQ) from P-CP-NP and C-R-HQ ternary systems, via multicomponent column adsorption on modified activated carbon (MAC), was evaluated in this study to determine the characteristic parameters of the column for ternary systems. A Taguchi L9 orthogonal array matrix was applied to investigate the effect of process parameters such as flow rate (Q), bed height (Z) and column diameter (D) on the breakthrough point of the process. The BET surface area of MAC was found to be 1245 m2/g. Higher flow rate, and lower bed height and diameter resulted in faster breakthrough. Statistical analysis of the data revealed that column diameter was the most significant factor (p

The present study reports an ultrasound-photocatalysis based hybrid method for effective degradation/mineralization of a bio-recalcitrant pharmaceutical pollutant, namely ofloxacin (OFLX). To understand the role of different techniques, individual and various combined ultrasound and ultraviolet along with H2O2, TiO2, and ZnO photo-catalyst were investigated in different protocols to understand synergistic effects and mechanistic insight of the mineralization process. Photocatalysts were characterized by FTIR, FE-SEM, TEM, EDX, BET, and EIS analysis. A significant synergistic index of 3.1 for mineralization of OFLX was obtained during the combined US/UV/H2O2/ZnO method due to higher oxidizing ( OH) radical formation as compared to other binary and ternary hybrid methods. OFLX degradation and total organic carbon removal were 94.2% and 45.1%, respectively, using US/UV/H2O2/ZnO method at operating condition of H2O2/OFLX stoichiometric molar ratio = 5, ZnO dosage = 0.40 g L−1, 40 kHz ultrasonic frequency, 125 W UV power, reaction time of 120 min and pH 6.3 (natural pH). Kinetics of the degradation was well-represented by the power-law kinetic model with an order of reaction being 2.2 and 1.9 for US + UV + H2O2 + TiO2 and US + UV + H2O2 + ZnO, respectively. Besides, specific energy consumption (SEC), electrical energy per order (EEO), and the operating cost (OC) of each method employed was determined. A detailed OFLX degradation pathway has been suggested, and possible reasons for synergy are identified and discussed.

In this paper, a hybrid advanced oxidation process of sonoelectrochemical, in which ultrasound and electrochemical are applied simultaneously, has been used for the degradation of ofloxacin (bio-recalcitrant pharmaceutical pollutant). Response surface methodology based central composite design was applied to understand the parametric effects of ultrasonic power, current density, initial pH, and electrolyte dose. Enhanced ofloxacin degradation was obtained using sonoelectrochemical (≈95%) process in comparison to the electrochemical (≈60.6%) and sonolysis alone (≈7.2%) after 120 min treatment time. Multi-response optimization was used so as to maximize COD removal (70.12%) and minimize specific energy consumption (11.92 kWh (g COD removed)−1)at the optimized parametric condition of pH = 6.3 (natural pH), ultrasonic power = 54 W, current density = 213 A m−2, and Na2SO4 electrolyte dose = 2.0 g L−1. It was revealed that •OH radicals contribute major to the ofloxacin degradation reaction among the other oxidizing agents. Degradation of the ofloxacin followed pseudo-first-order kinetics with a higher reaction rate, which confirmed the synergistic effect of 34% between ultrasound and electrochemical approaches. The degradation pathway of ofloxacin removal was elucidated at optimum condition by the temporal evolution of the intermediate compounds and final products using gas chromatography coupled with mass spectroscopy (GC-MS), liquid chromatography-mass spectroscopy (LC-MS), high-resolution mass spectroscopy (HR-MS), and Fourier transform infrared spectroscopy (FTIR). Atomic force microscopy (AFM) and field emission scanning electron microscope (FE-SEM) coupled with energy dispersed X-ray (EDX) were used to determine the morphology of electrodes. Operational cost analysis was done based on the reactor employed in the present study.

Advanced oxidation processes have gained attention recently due to their effectiveness in mineralizing toxic recalcitrant pollutants. In this paper, studies on combined sonolysis and electroxidation techniques have been reviewed for the degradation of the persistent organic pollutants, and real industrial wastewater. The effects of various parameters such as ultrasonic power, current density, initial pH, and electrolyte concentration have been elucidated. Critical analysis of the studies (1996-2020) on the treatment of various synthetic and real wastewater using the sono-electroxidation process has been considered. Ultrasound, in combination with electrochemical technology, is an attractive option for the treatment of industrial wastewater. The application of ultrasound gives the synergistic effect by virtue of the physical and chemical effects of cavitation. Coupling these two techniques increases the mineralization degree by increasing the mass transport rate and the chemical reaction rate, and reduce the electrode passivation and fouling problem. Woking with an optimized sonoelectrochemical reactor design with low power ultrasound with pulsed mode can remarkably decrease the energy cost and increase the economic viability of the treatment method. Challenges associated with the process are documented in this paper.

Present study investigates the direct and indirect electrochemical (EC) oxidation of malachite green (MG) dye in acidic and basic medium using RuO2–TiO2 and Pt coated Ti mesh electrodes (Ti/RuO2–TiO2 and Ti/Pt electrodes). The effects of process parameters such as current density (j), initial pH (pHo) and NaCl (electrolyte) concentration (m) during the EC oxidation were also examined. This study investigates the effect of dissolved chlorine, chlorate, chlorite, and chlorine dioxide formed during EC oxidation at different pH. Active sites of electrodes surface promote the production of OH radicals ( OH). Synergistic effect of active chlorine species and OH radicals significantly enhanced the indirect EC oxidation of MG dye solution with Ti/RuO2–TiO2 anode. Gas chromatography-mass spectrometry (GC–MS), high performance liquid chromatography (HPLC), color and chemical oxygen demand (COD) were used to identify the EC oxidative degradation mechanism with both electrodes. Acidic pH was found to promote the dye degradation. Under optimum condition, MG dye was completely decolorized and 98% COD removal was obtained after 140 min of EC treatment. Based on the intermediate and by-products identification, it seems that MG dye degradation occurred via N-methylation and conjugated structure destruction.

Jatropha curcas L. is a growing feedstock for biodiesel production. The first step in the exploitation of any plant for industrial application is to gather information about its chemistry, biology and all different applications so that the utilization of plant could be used optimized. J. curcas has been the centre of interest for many scientists in the past decade. The purpose of this paper is to present state-of-the-art review of J. curcas research advancement in biological, agronomical and biotechnological areas. This paper gives an overview on plantation science, composition, toxicity and genetics of J. curcas. This review also focuses on all J. curcas uses in agronomical terms. It gives a general idea of agricultural potential, utilizations, medical uses and other molecules that have been extracted from the plant. It finally focuses on the energy production from the crop and the biotechnological improvement of the biodiesel production process.

In this work, Ce–M catalysts (M = Co, Fe, Cu and Zn) synthesized by sol-gel method and characterized by various techniques have been evaluated for the transesterification of propylene carbonate (PC) with methanol for dimethyl carbonate (DMC) synthesis in a batch reactor. The catalysts were characterized by various techniques such as X-ray diffraction (XRD), N2-sorption analysis, scanning electron microscope (SEM-EDX) etc. Total basicity of CeCo, CeCu, CeZn and CeFe catalysts were 0.083, 0.698, 0.424 and 0.492 mmol/g with crystalline sizes found to be 19.4, 18.8, 9.6 and 21.6 nm, respectively. Best performing catalyst CeCu was further used for optimization of operating conditions such as methanol/PC molar ratio, catalysts dose, reaction time, reaction temperature and kinetics study. The reaction rate constant values as obtained using non-linear regression analysis were found to be 0.285, 0.570 1.255 and 1.596 h−1 at 120, 140, 160 and 180 °C, respectively for the CeCu catalyst. Reusability of the catalyst was studied in terms of PC conversion and turn over frequency.

This paper deals with the analysis of hazards associated with accidental release of high pressure from gas-pipeline transportation system. Simplified equations which are related to the fluid properties, operating pressure, the diameter of pipeline, hole or rupture diameter and the length of the pipeline have been used for the hazard analysis due to pipeline failure. The kind of release (i.e. leak) through a hole or the complete rupture was found not to affect the effective release rate because of an increase in the operating pressure. Among various gases, the release rate of butane with lower value of specific heat ratio (γ) is found to be always higher than that of propane and methane which have higher value of γ. Decay coefficient, defined as the ratio of release rate at any instant and to the initial maximum release rate, decreases with an increase in the leak (or hole) size. The accident affected distance increases with an increase in the hole size. During the leakage of natural gas and petroleum gas pipeline, affected distance of hazard is slightly higher for fire as compared to other events. The simplified models can be used with confidence to estimate the hazard distance or hazard area. The procedure developed will be helpful for safety management or emergency response planning for the pipeline transportation of the natural gas and petroleum gas.

Significant numbers of studies have been reported on use of various types of agricultural wastes as adsorbent. Teff straw originates from Ethiopia where chromium pollution is one of the major pollution problem. Therefore, in the present study, teff straw was tested as an adsorbent for hexavalent chromium removal from aqueous solution. Characterization of teff straw was done using various instruments such as X-ray diffraction, scanning electron micrograph (SEM) and Fourier transform infra-red (FTIR) spectroscopy. Batch experiments were carried out to study the effects like pH, initial chromium concentration, contact time and dose of teff straw on the efficiency of the adsorption process. Adsorption of Cr(VI) on teff straw adsorbent was by a complex process. Better realistic description of adsorption kinetics was seen from pseudo-second order rate equation. The equilibrium sorption characteristics of Cr(VI) from aqueous solutions with concentrations in the range of 100–900 mg/L were studied at different temperatures in the range of 288–318 K, and temperature increment was found to have a positive effect on the sorption process. Langmuir isotherm gave better representation over wide range of temperature. At adsorbent dose = 10 g/L, pH 2 and contact time = 6 h, maximum Cr(VI) uptake per unit mass of teff straw (qmax) was found as 58, 70, 79, and 86 mg/g at 288, 298, 308, and 318 K, respectively. The negative value of change in Gibbs free energy (ΔGo) indicated spontaneous adsorption of Cr(VI) onto teff straw adsorbent. Isosteric heats of adsorption ( Δ H st , a ) were low at low levels of surface coverage and increased progressively.

This paper presents an analysis and simulation of an accident involving a liquefied petroleum gas (LPG) truck tanker in Kannur, Kerala, India. During the accident, a truck tanker hit a divider and overturned. A crack in the bottom pipe caused leakage of LPG for about 20 min forming a large vapor cloud, which got ignited, creating a fireball and a boiling liquid expanding vapor explosion (BLEVE) situation in the LPG tank with subsequent fire and explosion. Many fatalities and injuries were reported along with burning of trees, houses, shops, vehicles, etc. In the present study, ALOHA (Area Locations of Hazardous Atmospheres) and PHAST (Process Hazard Analysis Software Tool) software have been used to model and simulate the accident scenario. Modeling and simulation results of the fireball, jet flame radiation and explosion overpressure agree well with the actual loss reported from the site. The effects of the fireball scenario were more significant in comparison to that of the jet fire scenario.

Utilization of carbon-do-oxide (CO 2 ) to produce alternative chemicals such as dimethyl carbonate (DMC) is one of the high priority areas of research. In this paper, ceria based catalyst were synthesized, characterized and used for DMC synthesis from CO 2 and methanol. Prepared catalyst was characterized by various techniques such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM), temperature programmed desorption (TPD) by NH 3 and CO 2 , Fourier transform infrared spectroscopy (FTIR) and N 2 adsorption–desorption. The catalytic activities were correlated with the basic and acidic properties of ceria catalyst for the synthesis of DMC in a batch reactor. The larger acidic and basic sites facilitated the DMC formation due to activation of methanol to methoxyl species and further reaction with CO 2 . Molecular sieve has been used as dehydrating agent to remove water, shift the thermodynamic equilibrium and facilitate higher DMC formation. Ceria catalyst showed DMC yield of 2.046 mmol DMC/g.cat at reaction temperature of 120 °C, pressure 150 bar and reaction time of 4 h.

In this study, reduced graphene oxide supported mesoporous zinc oxide (rGO@ZnO) was synthesized and applied for the photocatalytic mineralization of ofloxacin, an antibiotic, in the aqueous solution. In-situ rGO@ZnO nano-photocatalysts with different rGO content (0.2%, 0.5%, 1% and 2%) were synthesized using a reflux column method. The nano-photocatalyst was characterized by its structural (crystallinity), morphological, as well as optical properties with the help of powdered X-ray diffraction (P-XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectroscopy, Brauner Emmet Teller (BET), thermo-gravimetric/differential thermal analysis (TGA/DTA) and UV–vis diffuse reflectance spectroscopy (DRS). The influences of pH (5–9) and catalyst dose (400–1400 mg/dm3) with irradiation time were studied. At optimum conditions (0.5% rGO@ZnO dose of 1200 mg/dm3 for ofloxacin, pH = 7, and time = 300 min), ultimate degradation efficiency was found to be ≈99%, under UV light irradiation. The degradation kinetics fitted well with the first-order kinetic model. The photocatalytic mechanism of the enhanced photo-degradation in the presence of rGO was studied by comparing band structure with the potentials of the main reactive species ( O2− and OH), which result in the mineralization of ofloxacin. The intermediates and pathways during the mineralization were determined using liquid chromatography, which is coupled with mass spectrometry (LC–MS) analysis and a possible pathway was also proposed on the basis of identified intermediates.

Herein a new statistical approach based on Taguchi’s methodology was developed for optimizing continuous simultaneous adsorption of aniline (AN) and nitrobenzene (NB) from their binary aqueous solution in a column packed with granular activated carbon (GAC). Effects of column design parameters such as feed flow rate (Q), bed height (Z) and bed diameter (D) were studied for the breakthrough curve performance using Taguchi’s L9 orthogonal array design. The parameters were optimized at three levels with the higher-is-better type response characteristics. Further, the Thomas model was used to predict column breakthrough curve and breakthrough time. Higher sorption affinity of NB over AN towards GAC surface implied favorable attachment of NB molecules. Quicker breakthrough attainment was observed at higher Q, lower Z and lower D owing to faster saturation of sorption sites. Maximum individual equilibrium adsorption uptake for AN and NB was found to be 0.29 mg/g and 3.91 mg/g, respectively, at Q = 0.02 L/min, Z = 60 cm and D = 2.54 cm. The average total equilibrium adsorption uptake (qtot) from the experimental runs was found to be 4.2 mg/g which is closer to the predicted qtot value of 4.17 mg/g.

This study focuses on the photocatalytic degradation of quinoline, a recalcitrant heterocyclic nitrogenous aromatic organic compound, using the mixed oxide ZnO–TiO2 photo-catalyst. Photo-catalysts were synthesized by the solid-state reaction method at different calcination temperatures of 400 °C, 600 °C, and 800 °C. Different analytical methods, including Field emission scanning electron microscope, Brunauer-Emmett-Teller surface area, X-ray diffraction, UV–vis diffuse reflectance spectroscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy analysis were used for the catalyst characterization. The highest pore surface area of 57.9 m2g−1 was obtained for the photo-catalyst calcined at 400 °C. The effects of calcination temperature, solution pH, initial concentration, catalyst dose as well as irradiation time were studied. At the optimum condition, i.e., calcination temperature of 400 °C, pH ≈8 and catalyst dose of 2.5 gL−1, maximum quinoline degradation and total organic carbon (TOC) removal efficiency of ≈92% and ≈78% were obtained after 240 min for initial quinoline amount of 50 mgL−1. The 1st, 2nd, and nth-order kinetic models were applied to analyze the quinoline degradation rate. The photocatalytic mechanism was studied by drawing energy level diagram with the help of the band-gap structures of the ZnO and TiO2, potential of the free radicals like OH and O2 and HOMO-LUMO energy gap of the quinoline molecule. The proposed pathways of quinoline mineralization were suggested on the basis of the identified intermediates by the gas chromatograph-mass spectrometer analysis and scavenger study.