Catalytic hydrogenation of carbon dioxide (CO2) to methanol is an attractive way to recycle and utilize CO2. A series of Cu/ZnO/Al2O3/ZrO2 catalysts (CZAZ) containing different molar ratios of Cu/Zn were prepared by the co-precipitation method. The catalysts were characterized by temperature-programmed reduction (TPR), field emission scanning electron microscopy-energy dispersive x-ray analysis (FESEM-EDX) and X-ray diffraction (XRD). Higher surface area, SABET values (42.6-59.9 m2/g) were recorded at low (1) and high (5) Cu/Zn ratios with the minimum value of 35.71 m2/g was found for a Cu/Zn of 3. The reducibility of the metal oxides formed after calcination of catalyst samples was also affected due to change in metal-support interaction. At a reaction temperature of 443 K, total gas pressure of 3.0 MPa and 0.1 g/mL of the CZAZ catalyst, the selectivity to methanol decreased as the Cu/Zn molar ratio increased, and the maximum selectivity of 93.9 was achieved at Cu/Zn molar ratio of 0.33. With a reaction time of 3h, the best performing catalyst was CZAZ75 with Cu/Zn molar ratio of 5 giving methanol yield of 6.4%.
A copper-1,4-naphthalenedicarboxylic acid-based organic framework (Cu-NDCA MOF) with different morphologies was synthesized by solvothermal synthetic route via a simple protonation-deprotonation approach. The synthesized Cu-NDCA MOFs were analyzed by diverse microscopic and spectral techniques. The FE-SEM and TEM image results exhibited the flake-like (FL), partial anisotropic (PAT), and anisotropic (AT)-Cu-NDCA MOFs formation obtained at different pH (3.0, 7.0, and 9.0) of the reaction medium. The AT-Cu-NDCA MOF/GC electrode not only increases the electroactive surface area but also boosts the electron transfer rate reaction compared to other modified electrodes (PAT- and FL-Cu-NDCA MOFs/GCEs). Under the optimized conditions, the modified electrode (AT-Cu-NDCA MOF) exhibited a sharp oxidation peak (+ 0.46 V vs. Ag/AgCl) and higher current response for rutin. The electrode provides a wide linear range from 1 × 10-9 to 50 × 10-6 M, a low detection limit of 1.21 × 10-10 M, LOQ of 0.001 μM, and sensitivity of 0.149 μA μM-1 cm-2. The AT-Cu-NDCA MOF/GC electrode exhibited good stability (RSD = 3.52 ± 0.02% over 8 days of storage), and excellent reproducibility (RSD = 2.62 ± 0.02% (n = 3)). The modified electrode was applied to the determination of rutin in apple, orange, and lemon samples with good recoveries (99.79-99.91, 99.24-99.69, and 99.53-99.83, respectively). Graphical abstract Anisotropic structure of Cu-NDCA MOFs and its modification on glassy carbon electrode for ultra-sensitive determination of rutin in fruit samples.
Behaviors of cationic and nonionic mixed micelles in the form of hexadecyltrimethylammonium bromide (HDABr) and hexadecyltrimethylammonium bromide-Polyethylene glycol hexadecyl ether (C16E20), in the presence of inert salts (NaBr and 3,5-dichlorosodium benzoate), by the use of reaction probe between Pp and ionized PhSH (Pp = piperidine and PhSH = phenyl salicylate), has been reported in this work. The values of RXBr (RXBr denotes ion exchange constants obtained in the presence of micelles of different structural features) or KXBr (KXBr denotes ion exchange constants obtained in the presence of micelles of the same structural features) for 3,5-Cl2C6H3CO2- were almost the same at three different [HDABr]T (0.006, 0.010 and 0.015 M). The average value of RXBr or KXBr determined, in the presence of pure HDABr micelles, using semi empirical kinetic (SEK) method appeared to be almost 2½-fold larger (RXBr or KXBr = 198) than that in the presence of mixed HDABr-C16E20 micelles (RXBr or KXBr = 78). Rheological measurements indicated the existence of wormlike/twisted micelles and vesicle at 0.015 M pure HDABr, various [3,5-Cl2C6H3CO2Na], and 25 and 35℃ whereas there were evidence of only spherical micelles in the presence of mixed HDABr-C16E20 ([HDABr]T = 0.015 M and [C16E20]T = 0.006 M) at both temperatures.
In the present research work, dicationic ionic liquids, containing 1,4-bis(3-methylimidazolium-1-yl) butane ([C4(Mim)2]) cation with counter anions [(2HSO4)(H2SO4)0], [(2HSO4)(H2SO4)2] and [(2HSO4)(H2SO4)4] were synthesised. ILs structures were confirmed using 1H NMR spectroscopy. Thermal stability, Hammett acidity, density and viscosity of ILs were determined. Various types of lignocellulosic biomass such as rubber wood, palm oil frond, bamboo and rice husk were converted into levulinic acid (LA). Among the synthesized ionic liquids, [C4(Mim)2][(2HSO4)(H2SO4)4] showed higher % yield of LA up to 47.52 from bamboo biomass at 110°C for 60min, which is the better yield at low temperature and short time compared to previous reports. Surface morphology, surface functional groups and thermal stability of bamboo before and after conversion into LA were studied using SEM, FTIR and TGA analysis, respectively. This one-pot production of LA from agro-waste will open new opportunity for the conversion of sustainable biomass resources into valuable chemicals.
The synthesis of kojic acid derivative (KAD) from kojic and palmitic acid (C16:0) in the presence of immobilized lipase from Rhizomucor miehei (commercially known as Lipozyme RMIM), was studied using a shake flask system. Kojic acid is a polyfunctional heterocycles that acts as a source of nucleophile in this reaction allowing the formation of a lipophilic KAD. In this study, the source of biocatalyst, Lipozyme RMIM, was derived from the lipase of Rhizomucor miehei immobilized on weak anion exchange macro-porous Duolite ES 562 by the adsorption technique. The effects of solvents, enzyme loading, reaction temperature, and substrate molar ratio on the reaction rate were investigated. In one-factor-at-a-time (OFAT) experiments, a high reaction rate (30.6 × 10-3 M·min-1) of KAD synthesis was recorded using acetone, enzyme loading of 1.25% (w/v), reaction time of 12 h, temperature of 50 °C and substrate molar ratio of 5:1. Thereafter, a yield of KAD synthesis was optimized via the response surface methodology (RSM) whereby the optimized molar ratio (fatty acid: kojic acid), enzyme loading, reaction temperature and reaction time were 6.74, 1.97% (w/v), 45.9 °C, and 20 h respectively, giving a high yield of KAD (64.47%). This condition was reevaluated in a 0.5 L stirred tank reactor (STR) where the agitation effects of two impellers; Rushton turbine (RT) and pitch-blade turbine (PBT), were investigated. In the STR, a very high yield of KAD synthesis (84.12%) was achieved using RT at 250 rpm, which was higher than the shake flask, thus indicating better mixing quality in STR. In a rheological study, a pseudoplastic behavior of KAD mixture was proposed for potential application in lotion formulation.
Since bisphenol A (BPA) exhibits endocrine disrupting action and high toxicity in aqueous system, there are high demands to remove it completely. In this study, the BPA removal by sonophotocatalysis coupled with nano-structured graphitic carbon nitride (g-C3N4, GCN) was conducted with various batch tests using energy-based advanced oxidation process (AOP) based on ultrasound (US) and visible light (Vis-L). Results of batch tests indicated that GCN-based sonophotocatalysis (Vis-L/US) had higher rate constants than other AOPs and especially two times higher degradation rate than TiO2-based Vis-L/US. This result infers that GCN is effective in the catalytic activity in Vis-L/US since its surface can be activated by Vis-L to transport electrons from valence band (VB) for utilizing holes (h+VB) in the removal of BPA. In addition, US irradiation exfoliated the GCN effectively. The formation of BPA intermediates was investigated in detail by using high-performance liquid chromatography-mass spectrometry (HPLC/MS). The possible degradation pathway of BPA was proposed.
The theme of present research demonstrates performance of copper (II) sulfate (CuSO4) as catalyst in thermolysis process to treat reactive black 5 (RB 5) dye. During thermolysis without presence of catalyst, heat was converted to thermal energy to break the enthalpy of chemical structure bonding and only 31.62% of color removal. With CuSO4 support as auxiliary agent, the thermally cleaved molecular structure was further destabilized and reacted with CuSO4. Copper ions functioned to delocalize the coordination of π of the lone paired electron in azo bond, C=C bond of the sp2 carbon to form C-C of the sp3 amorphous carbon in benzene and naphthalene. Further, the radicals of unpaired electrons were stabilized and RB 5 was thermally decomposed to methyl group. Zeta potential measurement was carried out to analyze the mechanism of RB 5 degradation and measurement at 0 mV verified the critical chemical concentration (CCC) (0.7 g/L copper (II) sulfate), as the maximum 92.30% color removal. The presence of copper (II) sulfate catalyst has remarkably increase the RB 5 dye degradation as the degradation rate constant without catalyst, k1 is 6.5224 whereas the degradation rate constant with catalyst, k2 is 25.6810. This revealed the correlation of conversion of thermal energy from heat to break the chemical bond strength, subsequent fragmentation of RB 5 dye molecular mediated by copper (II) sulfate catalyst. The novel framework on thermolysis degradation of molecular structure of RB 5 with respect to the bond enthalpy and interfacial intermediates decomposition with catalyst reaction were determined.
Employment of edible oils as alternative green fuel for vehicles had raised debates on the sustainability of food supply especially in the third-world countries. The non-edible oil obtained from the abundantly available rubber seeds could mitigate this issue and at the same time reduce the environmental impact. Therefore, this paper investigates the catalytic cracking reaction of a model compound named linoleic acid that is enormously present in the rubber seed oil. Batch-scale experiments were conducted using 8.8 mL Inconel batch reactor having a cyclic horizontal swing span of 2 cm with a frequency of 60 cycles per minute at 450 °C under atmospheric condition for 90 min. The performance of HZSM-5, HBeta, HFerrierite, HMordenite and HY catalysts was tested for their efficiency in favouring gasoline range hydrocarbons. The compounds present in the organic liquid product were then analysed using GC-MS and classified based on PIONA which stands for paraffin, isoparaffin, olefin, naphthenes and aromatics respectively. The results obtained show that HZSM-5 catalyst favoured gasoline range hydrocarbons that were rich in aromatics compounds and promoted the production of desired isoparaffin. It also gave a higher cracking activity; however, large gaseous as by-products were produced at the same time.
In this work, natural sunlight successfully induced the deposition of gold (Au), silver (Ag), and palladium (Pd) nanoparticles (NPs) with 17.10, 9.07, and 12.70 wt% onto the surface of graphitic carbon nitride (g-C3N4). The photocatalytic evaluation was carried out by adopting Bisphenol A (BPA) as a pollutant under natural sunlight irradiation. The presence of noble metals was confirmed by EDX, HRTEM, and XPS analysis. The deposition of Ag NPs (7.9 nm) resulted in the degradation rate which was 2.15-fold higher than pure g-C3N4 due to its relatively small particle size, contributing to superior charge separation efficiency. Au/g-C3N4 unveiled inferior photoactivity because the LSPR phenomenon provided two pathways for electron transfer between Au NPs and g-C3N4 further diminished the performance. The improved degradation lies crucially on the particle size and Schottky barrier formation at the interface of M/g-C3N4 (M=Au, Ag, and Pd) but not the visible light harvesting properties. The mechanism insight revealed the holes (h+) and superoxide radical (•O2-) radical actively involved in photocatalytic reaction for all composites.
Visible light-responsive Pt-loaded coral-like BiFeO3 (Pt-BFO) nanocomposite at different Pt loadings was synthesized via a two-step hydrothermal synthesis method. The as-synthesized photocatalyst was characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), photoluminescence (PL) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and magnetic hysteresis loop (M-H loop) analyses. The FESEM images revealed that Pt nanoparticles were evenly distributed on the coral-like BFO. The UV-vis DRS results indicated that the addition of Pt dopant modified the optical properties of the BFO. The as-synthesized Pt-BFO nanocomposite was effectively applied for the photodegradation of malachite green (MG) dye under visible light irradiation. Specifically, 0.5 wt% Pt-BFO nanocomposite presented boosted photocatalytic performance than those of the pure BFO and commercial TiO2. Such a remarkably improved photoactivity could be mainly attributed to the formation of good interface between Pt and BFO, which not only boosted the separation efficiency of charge carriers but also possessed great redox ability for significant photocatalytic reaction. Moreover, the strong magnetic property of the Pt-BFO nanocomposite was helpful in the particle separation along with its great recyclability. The radical scavenger test indicated that hole (h+), hydroxyl (·OH) radical, and hydrogen peroxide (H2O2) were the main oxidative species for the Pt-BFO photodegradation of MG. Finally, the Pt-BFO nanocomposite was revealed high antibacterial activity towards Bacillus cereus (B. cereus) and Escherichia coli (E. coli) microorganisms, highlighting its potential photocatalytic and antibacterial properties at different industrial and biomedical applications.
Given that drugs and their degradation products are likely to occur as concoctions in wastewater, the degradation of a mixture of two nonsteroidal anti-inflammatory drugs (NSAIDs), diclofenac (DCF) and naproxen (NPX), was investigated by solar photolysis and titanium dioxide (TiO2)-mediated solar photocatalysis using an immersion-well photoreactor. An equimolar ratio (1:1) of both NSAIDs in distilled water, drinking water, and river water was subjected to solar degradation. Solar photolysis of the DCF and NPX mixture was competitive particularly in drinking water and river water, as both drugs have the ability to undergo photolysis. However, the addition of TiO2 in the mixture significantly enhanced the degradation rate of both APIs compared to solar photolysis alone. Mineralization, as measured by chemical oxygen demand (COD), was incomplete under all conditions investigated. TiO2-mediated solar photocatalytic degradation of DCF and NPX mixtures produced 15 identifiable degradants corresponding to degradation of the individual NSAIDs, while two degradation products with much higher molecular weight than the parent NSAIDs were identified by liquid chromatography mass spectrometry (LC-MS) and Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS). This study showed that the solar light intensity and the water matrix appear to be the main factors influencing the overall performance of the solar photolysis and TiO2-mediated solar photocatalysis for degradation of DCF and NPX mixtures.
Titanium dioxide (TiO2) has been considered a useful material for the treatment of wastewater due to its non-toxic character, chemical stability and excellent electrical and optical properties which contribute in its wide range of applications, particularly in environmental remediation technology. However, the wide band gap of TiO2 photocatalyst (anatase phase, 3.20 eV) limits its photocatalytic activity to the ultraviolet region of light. Besides that, the electron-hole pair recombination has been found to reduce the efficiency of the photocatalyst. To overcome these problems, tailoring of TiO2 surface with rare earth metals to improve its surface, optical and photocatalytic properties has been investigated by many researchers. The surface modifications with rare earth metals proved to enhance the efficiency of TiO2 photocatalyts by way of reducing the band gap by shifting the working wavelength to the visible region and inhibiting the anatase-to-rutile phase transformations. This review paper summarises the attempts on modification of TiO2 using rare earth metals describing their effect on the photocatalytic activities of the modified TiO2 photocatalyst.
Extensive contamination of soils by highly recalcitrant contaminants such as polycyclic aromatic hydrocarbons (PAHs) is an environmental problem arising from rapid industrialisation. This work focusses on the remediation of soil contaminated with 3- and 4-aromatic ring PAHs (phenanthrene (PHE) and fluoranthene (FLUT)) through catalysed hydrogen peroxide propagation (CHP). In the present work, the operating parameters of the CHP treatment in packed soil column was optimised with central composite design (H2O2/soil 0.081, Fe(3+)/soil 0.024, sodium pyrophosphate (SP)/soil 0.024, pH of SP solution 7.73). The effect of contaminant aging on PAH removals was also investigated. Remarkable oxidative PAH removals were observed for the short aging and extended aging period (up to 86.73 and 70.61 % for PHE and FLUT, respectively). The impacts of CHP on soil biological, chemical and physical properties were studied for both spiked and aged soils. Overall, the soil functionality analyses after the proposed operating condition demonstrated that the values for soil respiration, electrical conductivity, pH and iron precipitation fell within acceptable limits, indicating the compatibility of the CHP process with land restoration.
Silver nanoparticles (AgNPs) were prepared by reacting Kyllinga brevifolia extract (KBE) with AgNO3 aqueous solution at room temperature (22 ± 3 °C). The phytochemical constituents in KBE responsible for the reduction process were identified as carbohydrate, protein, and plant sterols (stigmasterol and campesterol). KBE was also found to function as a capping agent for stabilization of AgNPs. The AgNPs were stable at room temperature and had a quasi-spherical shape with an average particle size 22.3 nm. The use of KBE offers not only eco-friendly and non-pathogenic path for AgNPs formation, it also induced rapid formation of the AgNPs. Methylene blue (MB) removal was then done on the AgNPs in the presence of either KBE or NaBH4. Ninety-three percent removal of MB was achieved with a rate of reaction 0.2663 min-1 in the solution with KBE+AgNPs (pH 2). However, in NaBH4+AgNPs system, 100% MB removal was achieved at pH 8-10. The reaction rate was 2.5715 min-1 indicating a fast removal rate of MB dye. The process of reduction occurs via electron relay effect whereas in KBE+AgNPs system, sedimentation occurred along with the reduction process. Nevertheless, the use of KBE+AgNPs system is preferred as the reducing agent is more benign to the environment.
A cost-effective, facile hydrothermal approach was made for the synthesis of SnO2/graphene (Gr) nano-composites. XRD diffraction spectra clearly confirmed the presence of tetragonal crystal system of SnO2 which was maintaining its structure in both pure and composite materials' matrix. The stretching and bending vibrations of the functional groups were analyzed using FTIR analysis. FESEM images illustrated the surface morphology and the texture of the synthesized sample. HRTEM images confirmed the deposition of SnO2 nanoparticles over the surface of graphene nano-sheets. Raman Spectroscopic analysis was carried out to confirm the in-plane blending of SnO2 and graphene inside the composite matrix. The photocatalytic performance of the synthesized sample under UV irradiation using methylene blue dye was observed. Incorporation of grapheme into the SnO2 sample had increased the photocatalytic activity compared with the pure SnO2 sample. The electrochemical property of the synthesized sample was evaluated.
Polyhydroxyalkanoates (PHA), are biodegradable polyesters derived from many microorganisms such as the pseudomonads. These polyesters are in great demand especially in the packaging industries, the medical line as well as the paint industries. The enzyme responsible in catalyzing the formation of PHA is PHA synthase. Due to the limited structural information, its functional properties including catalysis are lacking. Therefore, this study seeks to investigate the structural properties as well as its catalytic mechanism by predicting the three-dimensional (3D) model of the Type II Pseudomonas sp. USM 4-55 PHA synthase 1 (PhaC1P.sp USM 4-55).
For environmental reasons, a new class of environmentally acceptable and renewable biolubricant based on vegetable oils is available. In this study, oxirane ring opening reaction of monoepoxide linoleic acid (MEOA) was done by nucleophilic addition of oleic acid (OA) with using p-toluene sulfonic acid (PTSA) as a catalyst for synthesis of 9(12)-hydroxy-10(13)-oleoxy-12(9)-octadecanoic acid (HYOOA) and the physicochemical properties of the resulted HYOOA are reported to be used as biolubricant base oils. Optimum conditions of the experiment using D-optimal design to obtain high yield% of HYOOA and lowest OOC% were predicted at OA/MEOA ratio of 0.30 : 1 (w/w), PTSA/MEOA ratio of 0.50 : 1 (w/w), reaction temperature at 110°C, and reaction time at 4.5 h. The results showed that an increase in the chain length of the midchain ester resulted in the decrease of pour point (PP) -51°C, increase of viscosity index (VI) up to 153, and improvement in oxidative stability (OT) to 180.94°C.
The Knoevenagel condensation is a powerful and primary step for the development of carbon-carbon bond transformations. These condensations offer versatile products/ intermediates for diverse uses in polymers, cosmetics, chemical industries, and medicinal chemistry. Various homogenous and heterogenous catalysts have been found to promote the Knoevenagel condensation reaction, both environmentally and economically. Due to their attractive use in the production of pharmaceutical drugs, they are proven to be the main force that drives the synthesis involving numerous multi-component and multistep reactions. The present study, therefore, aims to summarise reported Knoevenagel condensation reactions using metal-free catalysts resulting in pharmaceutically useful compounds with anti-cancer, anti-tumor, anti-oxidant, anti-malarial, anti-diabetic, and anti- bacterial activities. By considering factors like their structure-activity relationships (SARs), the reaction conditions, and the steps involved, as well as the advantages and limitations of the particular approach, we also provide a general framework and direction in order to achieve superior characteristics of the catalyst.
Microbial fuel cells (MFC) are emerging energy-efficient systems for copper (Cu) electrowinning from waste streams by coupling it with anodic oxidation of organics in wastewater. However, there is a lack of research examining scalable electrocatalysts for Cu electrowinning at low cathodic overpotentials in highly saline catholytes often found in e-waste leachates. The challenge of developing resilient anodic biofilms that withstand the antagonistic effects of ions migrating from catholytes in saline MFC also needs to be addressed. In this study, polypyrrole (PPy) cathodic electrocatalysts were developed and coupled with a robust halophilic anodic biofilm in MFC to improve the kinetics of Cu electrowinning from acidic chloride-based catholytes. Electrochemical characterisation of these cathodes revealed shuttling of electrons by redox-active PPy via the formation of intermediate Cu+-complexes as an energy-efficient pathway for producing metallic Cu. High power densities ranging from 0.63 ± 0.17 to 0.73 ± 0.05 W m-2 were achieved with undoped-PPy and phytic acid doped-PPy cathodes with simultaneous recovery of ∼97% Cu. These electrocatalysts also exhibited low charge transfer resistance (3-8 mΩ m2) that met the requisites for scalable cathodes in MFC. However, a decrease in the efficiency of PPy cathodes was observed over 5 d due to competing reactions at their interfaces, including re-oxidation of deposited Cu and cathodic corrosion, with further studies suggested to enhance their corrosion resistance. Nonetheless, integrating PPy electrocatalysts for Cu electrowinning in saline MFC has advanced its outlooks as an energy-efficient downstream process for urban mining of Cu from e-waste.
The thermoalkaline protease enzyme from pitaya (Hylocereus polyrhizus) waste was purified by a factor of 221.2 with 71.3% recovery using ammonium sulphate precipitation, gel filtration, and cation exchange chromatography. Gel filtration chromatography together with sodium dodecyl sulphate gel electrophoresis (SDS-PAGE) revealed that the enzyme is monomeric with a molecular weight of 26.7 kDa. The apparent K m and V max of the protease were 2.8 mg/mL and 31.20 u/min, respectively. The optimum pH and temperature were 8.0 and 70°C. The enzyme was highly active and stable over a wide pH range (from pH 3.0 to pH 11.0 with the optimum activity at pH 8.0). The protease has broad specificity toward azocasein, casein, hemoglobin, and gelatine. Activity of the enzyme was inhibited by Fe(2+) and Zn(2+), while protease activity was increased in the presence of Ca(2+) and Mg(2+) and Cu(2+) by factors of 125%, 110%, and 105%, respectively. The alkaline protease showed extreme stability toward surfactants and oxidizing agent. The purified protease exhibited extreme stability in the presence of organic solvents and inhibitors. In addition, the enzyme was relativity stable toward organic solvents and chelating agents, such as ethylenediaminetetraacetic acid (EDTA). The enzyme, derived from pitaya peel, possesses unique characteristics and could be used in various industrial and biotechnological applications.