Enhanced removal of As(III) and As(V) from water by a novel zirconium-chitosan modified spherical sodium alginate composite.

Most nano-scaled adsorbents have trouble in separating from aqueous solution, thus, a need for new materials of facile separation and predominant adsorption performance has arisen. This present study focused on a novel segregative zirconium-chitosan modified sodium alginate (Zr-CTS/SA) composite preparation and its performance for As(III/V) removal from aqueous solution. The obtained composite presented a spherical structure with a diameter of 2.0-3.0 mm and favorable thermal stability. Experimental data showed that Zr-CTS/SA had considerable adsorbability for As(III) and As(V), the adsorption capacities were enhanced about at least 20 and 6 times separately compared with pristine SA beads. The adsorption processes of As(III) and As(V) could both be described with Langmuir isotherm model and the maximum adsorption capacities reached 43.19 and 76.78 mg g-1, respectively. The kinetic data of As(III) followed the intra-particle diffusion model while As(V) fitted the pseudo-first-order model. Moreover, the adsorption mechanisms of As(III/V) involved ligand exchange with Cl on the surface of Zr-CTS/SA, another reaction pathway for As(V) was the electrostatic attraction with protonated -OH and -NH2 groups. Note that the employment of Zr-CTS/SA in low-concentration arsenic solution exhibited a residue concentration as low as the 10 µg L-1 WHO guideline for drinking water.

Fast and efficient phosphate removal on lanthanum-chitosan composite synthesized by controlling the amount of cross-linking agent.

In the present study, non-crosslinked lanthanum-chitosan (La-CTS-0X) and crosslinked lanthanum-chitosan (La-CTS-1X/2X) composites were prepared as new complex biosorbents for effective phosphate removal from wastewater. Batch adsorption experiments were investigated by varying the influencing parameters, viz., pH, initial concentration of phosphate ions, contact time, temperature and co-existing anions. Experimental data were well fitted to the Langmuir isotherm model (R2 = 0.9998) as well as the pseudo-second-order model (R2 = 1.000), indicating that the phosphate adsorption process was homogeneous, mono-layered and chemisorption dominated. Besides, the maximum phosphate adsorption capacity for La-CTS-0X/1X/2X was 47.28, 57.84 and 31.01 mg g-1 at pH 6, respectively. Thermodynamic parameters including ΔH° (-43.7 kJ mol-1), ΔS° (-132 J mol-1 K-1) and ΔG° (-4.60 kJ mol-1) revealed that the essence of adsorption was spontaneous and exothermic. The regenerated materials could be repeatedly used for three cycles without obvious degradation of performance. Characterization of the adsorbent using FTIR, SEM, EDS and XPS techniques suggested that the possible adsorption mechanisms were electrostatic attraction as well as ligand exchange. More importantly, the La-CTS-1X had rapid removal rate for phosphate within 10 min and the remained P concentration met the permissible limit by the U.S. Environmental Protection Agency (EPA).

Synthesis of spherical magnetic calcium modified chitosan micro-particles with excellent adsorption performance for anionic-cationic dyes.

In this present study, spherical magnetic calcium modified chitosan micro-particles (MG-Ca-CMPs) were synthesized by using embedding/cross-linking method and employed as an efficient adsorbent for Orange II (OII) in single system and coexisted with methylene blue (MB) in binary system. The obtained MG-Ca-CMPs were characterized by fourier transform infrared spectrometer, transmission electron microscopy, scanning electron microscope, X-ray diffraction and magnetic property measurement system analyses, which demonstrated that the MG-Ca-CMPs possessed core-shell structure and excellent superparamagnetic property. The adsorption behaviors for OII in single system and coexisted with MB in binary system were systematically studied. Adsorption experiments data showed that MG-Ca-CMPs presented an excellent high affinity to acid dye OII (qmax = 962 mg·g-1) in single system, which followed the Langmuir isotherm model and pseudo-second order kinetics model. Interestingly, MB, hardly adsorbed in acidic solution, had effective adsorption performance (increased from 20 mg·g-1 to 350 mg·g-1) in binary system by MG-Ca-CMPs. This result was attributed to the synergistic effect caused by the positive and negative charge attraction between OII and MB, forming the positive-negative-positive adsorption mechanism. It is believed that MG-Ca-CMPs could be used as a potential adsorbent for the adsorption and separation of coexisting anionic-cationic dyes from dye wastewater.