Multifunctional humate-based magnetic sorbent: Preparation, properties and sorption of Cu (II), phosphates and selected pesticides

Cerium(IV) chitosan-based hydrogel composite for efficient adsorptive removal of phosphates(V) from aqueous solutions

The excess presence of phosphate(V) ions in the biosphere is one of the most serious problems that negatively affect aqueous biocenosis. Thus, phosphates(V) separation is considered to be important for sustainable development. In the presented study, an original cerium(IV)-modified chitosan-based hydrogel (Ce-CTS) was developed using the chemical co-precipitation method and then used as an adsorbent for efficient removal of phosphate(V) ions from their aqueous solutions. From the scientific point of view, it represents a completely new physicochemical system. It was found that the adsorptive removal of phosphate(V) anions by the Ce-CTS adsorbent exceeded 98% efficiency which is ca. 4-times higher compared with the chitosan-based hydrogel without any modification (non-cross-linked CTS). The best result of the adsorption capacity of phosphates(V) on the Ce-CTS adsorbent, equal to 71.6 mg/g, was a result of adsorption from a solution with an initial phosphate(V) concentration 9.76 mg/dm3 and pH 7, an adsorbent dose of 1 g/dm3, temperature 20 °C. The equilibrium interphase distribution data for the Ce-CTS adsorbent and aqueous solution of phosphates(V) agreed with the theoretical Redlich-Peterson and Hill adsorption isotherm models. From the kinetic point of view, the pseudo-second-order model explained the phosphates(V) adsorption rate for Ce-CTS adsorbent the best. The specific effect of porous structure of adsorbent influencing the diffusional mass transfer resistances was identified using Weber-Morris kinetic model. The thermodynamic study showed that the process was exothermic and the adsorption ran spontaneously. Modification of CTS with cerium(IV) resulted in the significant enhancement of the chitosan properties towards both physical adsorption (an increase of the point of zero charge of adsorbent), and chemical adsorption (through the presence of Ce(IV) that demonstrates a chemical affinity for phosphate(V) anions). The elaborated and experimentally verified highly effective adsorbent can be successfully applied to uptake phosphates(V) from aqueous systems. The Ce-CTS adsorbent is stable in the conditions of the adsorption process, no changes in the adsorbent structure or leaching of the inorganic filling were observed.

Humic Acid-Modified Magnetite Nanoparticles for Removing [AuCl4]− in Aqueous Solutions

Humic acid-modified magnetite nanoparticle (MnP-HA) has been synthesized using the co-precipitation method and applied for removal of [AuCl4]−. Modifying of MnP-HA was prepared with the mass ratio of MnP-HA=10:1 and 10:3. The HA was extracted from peat soil of Sambutan Village, East Kalimantan, Indonesia, by the recommended procedure of the International Humic Substances Society (IHSS). The saturation magnetization of MnP-HA was decreased compared to unmodified MnP. The interaction between MnP and HA was occurred due to the chemical bond between Fe from MnP with the carboxylic group from HA. The coating HA on the surface of MnP unchanged the formation of the crystal structure of MnP and increased the particle size. The optimum removal of [AuCl4]− on MnP and MnP-HA materials was optimum at pH 3.0. The Langmuir isotherm model with sorption capacity was 0.23, 4.85, and 4.65 mol g–1 for MnP, MnP-HA=10:1, and 10:3, respectively. Using a pseudo-second-order equation, the degradation of the kinetics model of [AuCl4]− on MnP, MnP-HA=10:1 and 10:3 with adsorption rate constant (k) were 0.02, 0.07, and 0.06 g.mol min–1.

Investigating the potential of synthetic humic-like acid to remove metal ions from contaminated water

Humic acid can effectively bind metals and is a promising adsorbent for remediation technologies. Our studies initially focussed on Cu²⁺ as a common aqueous contaminant. Previous studies indicate that carboxylic groups dominate Cu²⁺ binding to humic acid. We prepared a synthetic humic-like acid (SHLA) with a high COOH content using catechol (0.25 M) and glycine (0.25 M) with a MnO₂ catalyst (2.5% w/v) at pH = 8 and 25 °C and investigated the adsorption behaviour of Cu²⁺ onto it. The SHLA exhibited a range of adsorption efficiencies (27%-99%) for Cu²⁺ depending on reaction conditions. A pseudo-second-order kinetic model provided the best fit to the experimental data (R² = 0.9995-0.9999, p ≤ 0.0001), indicating that chemisorption was most likely the rate-limiting step for adsorption. The equilibrium adsorption data showed good fits to both the Langmuir (R² = 0.9928-0.9982, p ≤ 0.0001) and Freundlich (R² = 0.9497-0.9667, p ≤ 0.0001) models. The maximum adsorption capacity (q_m) of SHLA increased from 46.44 mg/g to 58.78 mg/g with increasing temperature from 25 °C to 45 °C. Thermodynamic parameters (ΔG⁰ = 2.50-3.69 kJ/mol; ΔS⁰ = 0.06 kJ/(mol·K); ΔH⁰ = 15.23 kJ/mol) and values of R_L (0.0142-0.3711) and n (3.264-3.527) show that the adsorption of Cu²⁺ onto SHLA was favourable, spontaneous and endothermic in nature. Over six adsorption/desorption cycles using 0.5 M HCl for the desorption phase, there was a 10% decrease of the adsorption capacity. A final experiment using a multi-metal solution indicated adsorption efficiencies of up to 84.3-98.3% for Cu, 86.6-98.8% for Pb, 30.4-82.9% for Cr, 13.8-77.4% for Ni, 9.2-62.3% for Cd, 8.6-51.9% for Zn and 4.6-42.1% for Co. Overall, SHLA shows great potential as an adsorbent to remove metals from water and wastewater.