In this study, the viability of using calcined cocoa pod husk ash (CCPHA) as a catalyst for the transesterification of neem seed oil (NSO) into biodiesel was investigated. Prior to transesterification to biodiesel, the oil was pretreated with Fe 2 (SO 4 ) 3 via esterification to reduce its high acid value content. The Box-Behnken design (BBD) and central composite design (CCD) of response surface methodology (RSM) were used to investigate the individual and interactive effects of the methanol/ oil ratio, catalyst amount, and reaction time on the acid value and biodiesel yield, respectively. Results of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and elemental analysis showed that the catalytic action of the CCPHA produced was due to its K content and microstructural development when calcined at 700 °C for 4 h. The acid value of the NSO could be reduced from 11.57 to 1.80 mg of KOH/g of oil using optimum values of the methanol/oil ratio of 2.19 (v/v), catalyst amount of 6 wt %, and reaction time of 15 min while maintaining the reaction temperature constant at 65 °C. The results confirmed that neem seed oil methyl ester (NSOME), which satisfied ASTM D6751 and EN 14214 standards, could be produced at an optimum yield of 99.3 wt % using the methanol/oil ratio of 0.73 (v/v), catalyst amount of 0.65 wt %, and reaction time of 57 min while maintaining the reaction temperature constant at 65 °C. The results of this study demonstrated the prospect of developing an heterogeneous base catalyst from cocoa pod husk (CPH) for biodiesel production, which may reduce the total cost of production.

Application of solid catalysts synthesized from agricultural wastes provides an environmentally benign and low-cost process path to synthesize biodiesel. An ash containing an equal mixture of cocoa pod husk, plantain peel and kola nut pod husk ashes (CPK) was obtained by open combustion of each of the biomass in air and calcined at 500 °C for 4 h. The calcined CPK ash was characterized to determine its catalytic potential. Two-level transesterification technique was used to synthesize biodiesel using the developed catalyst. The process parameters involved were optimized for the microwave-aided transesterification of a blend of honne, rubber seed and neem oils in a volumetric ratio of 20:20:60, respectively. The study showed that the ash derived from combination of the biomass wastes provided a catalyst which consists all necessary catalytic ingredients in their relative abundance. The calcined CPK consists of 47.67% of potassium, 5.56% calcium and 4.21% magnesium attesting to its heterogenous status. The physisorption isotherms reveals that it was dominantly mesoporous in structure and made up of nanoparticles. A maximum of 98.45 wt.% biodiesel was obtained from a MeOH:oil blend of 12:1, CPK concentration of 1.158 wt.% and reaction time of 6 min under microwave irradiation. The quality of the synthesized biodiesel satisfied the requirements stipulated by standard specifications. Thus, this work demonstrates that a blend of agrowastes and mixtures of non-edible oils could be used to synthesize good quality and sustainable biodiesel that can replace fossil diesel.

Polyacrylonitrile and its TiO 2 composites were electrospun into nanofibers in N, N'-dimethylformamide for photocatalysis and antifouling experiments. The resultants nanofibers were characterized using field emission scanning microscope, Fourier transform infrared spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy and contact angle analyses. Fourier transform infrared spectroscopy confirmed the formation of polyacrylonitrile-TiO 2 composite nanofibers with their diameter ranging from 10 to 340 nm. The x-ray photoelectron spectroscopy results indicate the formation of O-Ti-C bonds on polyacrylonitrile-TiO 2 matrix. polyacrylonitrile-TiO 2 and polyacrylonitrile nanofiber surfaces showed superhydrophobicity with water contact angle of 155 ± 1 and 154 ± 1, respectively at 120 s. The photocatalytic properties of polyacrylonitrile nanofibers and polyacrylonitrile-TiO 2 nanofibers were investigated under a simulated visible light source of 1000 W/m 2 using methylene blue. About 90% of methylene blue was degraded within 3 h of exposure using polyacrylonitrile-TiO 2 nanofibers while 55% methylene blue degradation was achieved for polyacrylonitrile nanofibers. Photoluminescence experiment conducted on both materials showed that polyacrylonitrile-TiO 2 could produce OH radicals 10-fold compared to polyacrylonitrile nanofibers. Antimicrobial tests were conducted using E. coli and Bacillus sp. The results showed that only polyacrylonitrile-TiO 2 under visible light hindered the growth of these bacteria with a greater effect on the Gram-positive bacterium, Bacillus sp. The photo-degradation and microbial growth inhibition properties of polyacrylonitrile-TiO 2 showed that the material could be used as an antifouling material under visible light.

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a b s t r a c tThe rare-earth elements (REEs) remain very important due to the growing increase in their demand and for their critical and indispensable use in many high-tech industries today. This growing demand for REEs has led to an increased environmental exposure and water pollution from numerous REEs commercial products and as a result, the recovery of REEs is a significant issue that requires appropriate consideration. There are diverse and various strategic techniques available to remove metal ions from aqueous solutions, but nanofiber adsorbent appears to be quite innovative due to their outstanding characteristics such as cost effectiveness, flexibility, high surface area, porosity, and the portable nature which makes them a better choice for potential adsorbent applications. This review presents a brief view on several typical removal techniques, new developments and applicable examples of the various technologies used for the removal of rare earth elements from water/ wastewater solutions. The review highlights these developments with a particular focus on innovative physicochemical removal processes like adsorption as the process techniques most widely used.

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