A composite based on hydroxyapatite biocrystal and poly(aniline-o-phenylenediamine) copolymer for efficient removal of anionic dyes from wastewater

Abstract

BackgroundAcid dyes in any water source strongly impact its color, blocking sunlight and harming aquatic life. Herein, the technical applicability of a novel composite based on hydroxyapatite and poly(aniline-o-phenylenediamine) for removing dyes from synthetic wastewater was investigated using a batch method. MethodsIn this work, camel bones were used as a source of hydroxyapatite. Camel bones were pretreated in an alkali environment before extracting hydroxyapatite biocrystal (HAP). Subsequently, the extracted HAP was mixed with the poly(aniline-o-phenylenediamine) (PANI@PoPD) co-polymer. Different formulation methods were designed to optimize the tested composite samples' shape, size, structure and composition. Then, the optimized composite was further used as an adsorbent to remove orange G (OG) and thymol blue (TB) dyes from synthetic wastewater. The effects of the composite's dose, pH, dyes’ initial concentration and temperature on the overall performance of the composite were assessed. Statistical tests were then used to test the best experimental conditions to remove target dyes from wastewater. Significant findingsBy keeping the dye concentration constant at 50 mg/L for both OG and TB in wastewater at 25 °C, pH = 2 and 800 rpm of agitation speed in a batch reactor, it was found that the synthesized composite efficiently removes 99% of each dye at optimum dose of 0.5 or 1 g/L with a reaction time close to 30 or to 80 min for OG or TB, respectively. The predictive capacity of two-parameter models, including the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models, and three-parameter models such as the Redlich-Peterson, Sips and Toth models, was assessed to estimate the collected adsorption data. It was found that the statistical analysis was slightly better when the Temkin model was applied. This indicates that this equation was better suited to represent the experimental data of the adsorption of the OG dye. In contrast, the Redlich-Peterson and Toth models were in better agreement with the experimental results of the TB dye adsorption. Furthermore, thermodynamic parameters associated with each dye adsorption demonstrated its feasibility, while the adsorption kinetic data were found to be better described with the pseudo-second-order kinetics. In addition, the regenerability performances of the tested composite were successfully assessed by reusing the spent composite five consecutive times.