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In the present study, pectin-alginate-titania (PAT) composites were synthesized and the adsorptive removal behavior of methylene blue (MB) from aqueous solution, as a model of synthetic organic effluents, onto the prepared PAT composites were investigated by monitoring the effect of contact time, initial MB concentration, and temperature. The adsorption isotherm data were fitted well with the Freundlich isotherm model, suggesting the surface heterogeneity of the PAT composites and that the MB adsorption occurred on the active sites on multilayer surface of the composites. The adsorption kinetics of MB was demonstrated to be pseudo-second order, governed by two intraparticle diffusion rates, and the adsorption process was exothermic, spontaneous, and more disorder. The Langmuir isotherm model suggested that the maximum adsorption capacity of MB on the PAT composites was in the range of 435–637 mg g–1. In general, it increased with the TiO2 NPs content in the PAT composites, due most likely to the increase in surface area exposing more functional groups of the pectin and alginate to interact with the synthetic dye. The adsorptive removal of MB by the PAT composites was found to be more efficient compared with many other reported adsorbents, such as graphene oxide hybrids, pectin microspheres, magnetite-silica-pectin composites, clay-based materials, chemically treated minerals, and agricultural waste. The present study therefore demonstrated for the first time that PAT composites are not only promising to be utilized as an adsorbent in wastewater treatment, but also provide an insight into the adsorption mechanism of the synthetic dyes onto the biopolymers-titania composites. Graphic abstract Insight into the adsorption kinetics, mechanism, and thermodynamics of methylene blue from aqueous solution onto pectin-alginate-titania composite microparticles.

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Citrus maxima white pith was utilized for the isolation of pectin under acidified condition using L-(+)-tartaric acid, at extraction pH in the range of 1.0 and 2.0. The extraction yield and physicochemical properties (ash content, equivalent weight, methoxy content, anhydrouronic acid, degree of esterification) of the isolated pectin was investigated. The highest yield (70.2%) obtained in this extraction was at pH 1.0, 60°C, 120 minutes. The optimized condition of the isolated pectin in this study was based on the yield and physicochemical properties, where pectin extracted at pH 2.0 and 6080°C for 60120 minutes resulted in a 59.6% yield, with low ash content (2.82%), highest equivalent weight (1098.8) for gelling effect and highest DE (39.2%). The findings are within the range for a good quality pectin. The FTIR spectra of the isolated pectin at different pH mediums, but at constant temperature of 70°C and extraction time of 60 minutes were compared. The presence of methyl esterified carboxyl (1696 cm-1) and carboxylate group confirms the presence of pectin. This isolated pectin as an innovative raw material is potentially applicable for adsorbents, thin films, environmentally-friendly agents and green corrosion inhibitors.

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