The rectorite/carbon composites: Fabrication, modification and adsorption

Biopolymer Meets Nanoclay: Rational Fabrication of Superb Adsorption Beads from Green Precursors for Efficient Capture of Pb(II) and Dyes

Renewable, green, and safe natural biopolymer-derived materials are highly desired for the purification of pollutants, but significantly improving their performance without the introduction of additional harmful chemicals remains a huge challenge. Based on the concept of "structure optimization design", environment-friendly composite beads (named SA/PASP/RE) with excellent adsorption performance and recyclability were rationally constructed through a green ionic crosslinking route, using the completely green biopolymer sodium alginate (SA), sodium salt of polyaspartic acid (PASP), and the natural nanoclay rectorite (RE) as starting materials. The nano-layered RE was embedded in the polymer matrix to prevent the polymer chain from becoming over-entangled so that more adsorption sites inside the polymer network were exposed, which effectively improved the mass transfer efficiency of the adsorbent and the removal rate of contaminants. The composite beads embedded with 0.6% RE showed high adsorption capacities of 211.78, 197.13, and 195.69 mg/g for Pb(II) and 643.00, 577.80, and 567.10 mg/g for methylene blue (MB) in Yellow River water, Yangtze River water, and tap water, respectively. And the beads embedded with 43% RE could efficiently adsorb Pb(II) and MB with high capacities of 187.78 mg/g and 586.46 mg/g, respectively. This study provides a new route to design and develop a green, cost-effective, and efficient adsorbent for the decontamination of wastewater.

Development of carbon adsorbents with high surface acidity and basicity from polyhydric alcohols with phosphoric acid activation for Ni(II) removal

In this study, polyhydric alcohols, including glycerol, erythritol, xylitol, mannitol, and inositol, were chosen as carbon precursors for preparation of carbon adsorbents via phosphoric acid activation. The thermal behaviors of phosphoric acid-treated polyhydric alcohols revealed the formation and decomposition of organic phosphates at low temperatures, which enhanced the creation of functional groups on activated carbon. In general, the activated carbons showed relative low surface area (the highest one of 509 m²/g for AC-xylitol) due to the low activation temperature, and low yields (the highest one of 36.6% for AC-xylitol) due to the volatilization and decomposition of organic phosphates. The activated carbons contained 50-90% larger total amount of surface groups than the reference activated carbon derived from lignocellulose material, which mainly resulted in their 40-75% higher Ni(II) adsorption capacity. These results also indicated that the polyhydric alcohols-based activated carbons can be promising candidates for Ni(II) removal.

Green preparation of a novel red mud@carbon composite and its application for adsorption of 2,4-dichlorophenoxyacetic acid from aqueous solution

This study reports the eco-friendly preparation of a novel composite material consisting of red mud and carbon spheres, denoted as red mud@C composite, and its application for the removal of 2,4-dichlorophenoxyacetic acid herbicide (2,4-D) from aqueous solution. The preparation route has a green approach because it follows the low-energy consuming one-step hydrothermal process by using starch as a renewable carbon precursor and red mud as a waste from aluminum production industry. Characterization of the red mud@C composite was performed by FT-IR, TGA, SEM, TEM, BET, XRD, and Raman microscopy analyses. The batch adsorption studies revealed that the red mud@C composite has higher 2,4-D adsorption efficiency than those of the red mud and the naked carbon spheres. The maximum removal at initial pH of 3.0 is explained by considering the pKa of 2,4-D and pH of point of zero charge (pH_pzc) of the composite material. The adsorption equilibrium time was 60 min, which followed the pseudo-second-order kinetic model together with intra-particle diffusion model. The isotherm analysis indicated that Freundlich isotherm model better represented the adsorption data, with isotherm parameters of k [15.849 (mg/g) (mg/L)^-1/n ] and n (2.985). The prepared composite is reusable at least 5 cycles of adsorption-desorption with no significant decrease in the adsorption capacity.

Porous cellulose spheres: Preparation, modification and adsorption properties

Porous cellulose spheres (PCS) were fabricated by precipitating the spheres from a cellulose ionic liquid solution, followed by freezing, solvent exchange, and drying. PCS had low crystallinity and a large surface area that facilitated modification with trisodium trimetaphosphate (STMP) to introduce phosphate ester groups into the porous structure of the heterogeneous system. The STMP-modified PCS (SPCS) were used to remove heavy metal ions from aqueous solution. With increasing STMP dosage, the adsorption capacity of SPCS obviously improved due to chelation between Pb²⁺ and phosphate ester groups. The kinetic adsorption and isotherm data matched the pseudo-second order model and the Langmuir model well. The maximum adsorption capacity reached 150.6 mg g^-1 for SPCS. SPCS were competitive with other absorbents because the phosphate ester groups and porous structure contributed to Pb²⁺ adsorption. Moreover, SPCS can be regenerated with ethylenediamine tetraacetic acid disodium salt (EDTA) solution for repetitious adsorption of Pb²⁺.