Synthesis and characterization of Zr(IV) doped immobilized cross-linked chitosan/perlite composite for acid orange II adsorption.

To enhance the adsorption capacity of chitosan for acid orange II (AOII) adsorption, a novel adsorbent, zirconium(IV) doped immobilized cross-linked chitosan/perlite (Zr(IV)-CS-PT) composite was synthesized and characterized. Batch studies were conducted to analyze the effect of different parameters on AOII adsorption, such as Zr (IV) loading amount, pH, adsorbent dosage and temperature. Also, kinetic data revealed that AOII adsorption was well described by pseudo-second order kinetic model. Langmuir adsorption isotherm model was best described the isotherm data and maximum adsorption capacity was found 476.2 mg/g at natural pH. The thermodynamic data showed that the AOII adsorption occurred spontaneously and endothermic nature. Desorption and recycle experiments showed that after six cycle the adsorption efficiency was decreased from 95.6% to 90.1%, which shows the Zr(IV)-CS-PT is a reusable, cost-effective and high adsorption capacity adsorbent.

Determination of total antioxidant capacity of humic acids using CUPRAC, Folin-Ciocalteu, noble metal nanoparticle- and solid-liquid extraction-based methods.

Total antioxidant capacity (TAC) of humic acid (HA) samples was determined using CUPRAC (CUPric Reducing Antioxidant Capacity), FC (Folin-Ciocalteu), QUENCHER-CUPRAC, QUENCHER-FC, Ag-NP (Silver nanoparticle)‒ and Au-NP (Gold nanoparticle)‒based methods. Conventional FC and modified FC (MFC) methods were applied to solid samples. Because of decreased solubility of Folin-Ciocalteu's phenol reagent in organic solvents, solvent effect on TAC measurement was investigated using QUENCHER-CUPRAC assay by using ethanol:distilled water and dimethyl sulfoxide:distilled water with varying ratios. To see the combined effect of solubilization (leaching) and TAC measurement of humic acids simultaneously, QUENCHER experiments were performed at 25°C and 50°C; QUENCHER-CUPRAC and QUENCHER-FC methods agreed well and had similar precision in F-statistics. Although the Gibbs free energy change (ΔG°) of the oxidation of HA dihydroxy phenols with the test reagents were negative, the ΔG° was positive only for the reaction of CUPRAC reagent with isolated monohydric phenols, showing CUPRAC selectivity toward polyphenolic antioxidants. This is the first work on the antioxidant capacity measurement of HA having a sparingly soluble matrix where enhanced solubilization of bound phenolics is achieved with coupled oxidation by TAC reagents.