Hydrothermal Synthesis of Amino-PVC/DE Composite and Its Adsorption Performance for Formaldehyde

Surface Structure Analysis and Formaldehyde Removal Mechanism of Lotus Shell Biochar: An Experimental and Theoretical Perspective

The adsorption of gaseous HCHO by raw lotus shell biochar carbonized at 500, 700, and 900 °C from the perspective of its internal crystal structure and surface functional groups was investigated by an integrated approach of experiments and density functional theory calculations. The results showed that lotus shell biochar carbonized at 700 °C had the best adsorption effect at a HCHO concentration of 10.50 ± 0.30 mg/m³, with an adsorption removal rate of 87.64%. The HCHO removal efficiency by lotus shell biochar carbonized at 500 and 900 °C was determined to be 80.96 and 83.07%, respectively. The HCHO adsorption on lotus shell biochar carbonized at 700 °C conformed to pseudo-second-order kinetics and was predominantly controlled by chemical adsorption. The Langmuir isotherm was the underlying mechanism for the monomolecular layer adsorption with a maximum adsorption capacity of 0.329 mg/g. The density functional theory calculations revealed that the adsorption of HCHO on the surface of CaCO₃ and KCl in lotus shell biochar carbonized at 700 °C was a chemical adsorption process, with adsorption energies ranging from -64.375 to -87.554 kJ/mol. The strong interaction between HCHO and the surface was attributed to the electron transfer from HCHO to the surface, facilitated by metal atoms (Ca or K) and the oxygen atoms of HCHO. The carboxyl group on the surface of lotus shell biochar carbonized at 700 °C was identified as the key functional group responsible for HCHO adsorption. This study advanced our understanding of the environmental functions of inorganic crystals and surface functional groups in raw biochar and will enable the further development of biochar materials in environmental applications.

Self-regulated immobilization behavior of multiple heavy metals via zeolitization towards a novel hydrothermal technology for soil remediation

More efficient soil remediation technologies are highly anticipated to treat large quantities of heavy metal-polluted urban sites nowadays. Herein, a novel hydrothermal technology of converting heavy metal-polluted soils into zeolites for in-situ immobilizing heavy metals was proposed. The zeolites (analcime and cancrinite) could be synthesized hydrothermally with certain Na/Si and Al/Si ratios. The formed zeolites could manage to change their species and structure during zeolitization to accommodate different heavy metals in soil according to their size and charge. Since smaller-size Cu²⁺ was introduced, analcime and some cancrinite possessing small cages could be formed adaptively to immobilize the Cu²⁺ by replacing Na⁺ and forming Cu²⁺-OH and Cu²⁺-O. Whereas, cancrinite with large channels managed to form to immobilize the larger-size Cd²⁺ by forming Cd²⁺-O. Interplanar spacing variation of zeolites also corresponded to their structural change for accommodating different heavy metals. Leaching results showed the amounts of Cu and Cd leached from the synthesized zeolites were reduced to 0.005% and 0.05% respectively, reflecting a more stable immobilization of smaller heavy metals by small cages, in agreement with the results of distribution coefficient (K_d). Negligible effect of pH environment on the leaching rates further confirmed the stable structural immobilization of heavy metals by zeolites.

Acid-Modified Sepiolite-Supported Pt (Noble Metal) Catalysts for HCHO Oxidation at Ambient Temperature

The critical need to enhance the quality of indoor air leads to the improvement of catalyst activity for the removal of formaldehyde. Sepiolite can be utilized in catalytic reactions for its unique structure, composition and high surface area. The adhesion between sepiolite fibers and the blocked microporous channel (by impurities) demands the activation of natural sepiolite through acid treatment. This treatment successfully produces acid-modified sepiolite Pt-supported samples. The impacts of different acid concentrations, Pt loading content and calcination temperature on catalytic activity for formaldehyde (HCHO) oxidation are studied. The catalytic activity of HCHO is characterized and evaluated by techniques including specific surface area, X-ray diffraction, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy and transmission electron microscopy. The results show the maximum specific area of sepiolite at the optimized 0.06 M acid concentration. Among all the prepared samples, the 0.02Pt/Sep catalyst calcined at 500 °C exhibits the highest catalytic activity for the oxidation of HCHO.