Highly selective adsorption of Hg (II) from aqueous solution by three-dimensional porous N-doped starch-based carbon

Schiff base functionalized dialdehyde starch for enhanced removal of Cu (II): Preparation, performances, DFT calculations

Dialdehyde starch modified by 2-hydrazinopyridine (HYD-DAS) based on the reaction of dialdehyde starch (DAS) and 2-hydrazinopyridine was synthesized and characterized by FT-IR spectra, element analysis and SEM. HYD-DAS can efficiently adsorb Cu (II) ion to demonstrate visual color changes from yellow to dark brown in aqueous solutions. The influence on HYD-DAS to Cu (II) adsorption including pH value of solution, isotherm, kinetics, thermodynamics and possible mechanism had also been examined. Batch experiments indicate that HYD-DAS's to Cu (II) adsorption reaches equilibrium within 250 min, and its adsorption capacity and rate are 195.75 mg/g and 98.63 %, respectively. Moreover, HYD-DAS to Cu (II) adsorption remains robust and underscoring after five cycles to exhibit good selectivity and reusability. Kinetics studies suggest the absorption process follows a quasi-second-order with isotherms aligning to the Langmuir monolayer model, and thermodynamics reveals that it is a spontaneous endothermic nature of adsorption. Based on the analyses of XPS and DFT calculations, a possible mechanism for HYD-DAS to Cu (II) adsorption is that Cu (II) combined with nitrogen atoms from Schiff base and hydrazine pyridine ring in HYD-DAS.

Starch modified NiFe layered double hydroxide composites for better adsorption and photocatalytic removal of reactive dye and piroxicam-20 drug

One of the most omnipresent problems to the environment is the efficient removal of textile dyes and non-steroidal drugs from wastewater. For this purpose, renewable, sustainable, and biodegradable biopolymers are used. In this study, starch (S) modified NiFe-layered double hydroxide (LDH) composites were successfully synthesized by the co-precipitation method and have been examined as a catalyst for the effective adsorption of reactive blue 19 dye, reactive orange 16 dye, and piroxicam-20 NSAID from wastewater and photocatalytic degradation of reactive red 120 dye. The physicochemical properties of the prepared catalyst were assessed by XRD, FTIR, HRTEM, FE-SEM, DLS, ZETA, and BET. The coarser and more porous micrographs are shown in FESEM, indicating the homogeneous dispersion of layered double hydroxide on starch polymer chains. The S/NiFe-LDH composites have a slightly greater S_BET (6.736 m²/g) than NiFe LDH (4.78 m²/g). The S/NiFe-LDH composite shows remarkable ability in the removal of reactive dyes. The band gap value of NiFe LDH, S/NiFe LDH (0.5:1), and S/NiFe LDH (1:1) composites was calculated as 2.28 eV, 1.80 eV, and 1.74 eV, respectively. The q_max assessed from Langmuir isotherm for removal of piroxicam-20 drug, reactive blue 19 dye, and reactive orange 16 was 2840 mg/g, 149.47 mg/g, and 182.4 mg/g, respectively. The activated chemical adsorption without product desorption is predicted by the Elovich kinetic model. With reactive red 120 dye, S/NiFe-LDH shows photocatalytic degradation within 3 h of irradiation of visible light with 90% removal efficiency and follows a pseudo-first-order kinetic model. The scavenging experiment confirms the involvement of electrons and holes in photocatalytic degradation. With a little decline in adsorption capacity up to five cycles, starch/NiFe LDH was easily regenerated. So, the suitable adsorbent required for wastewater treatment is nanocomposites of LDHs and starch as they enhance the chemical and physical attributes of the composite structure with greater absorption capabilities.