Chao-Rong Chen

Influences of a glycerin co-solvent on the compatibility of MgAl hydrotalcites with a polypropylene matrix

Hydrotalcites as flame retardants for industrial applications require good compatibility with polymers. Glycerin co-solvent was employed during the precipitation of MgAl hydrotalcite (Mg/Al-HT) particles and the dispersion of the Mg/Al-HT particles in a polypropylene (PP) matrix was studied. The microstructures, textural and surface properties of the hydrotalcites were contrastively investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, laser particle size analysis, Barrett–Joyner–Hallender/Brunauer–Emmett–Teller methods (BJH/BET), and thermogravimetric and differential thermal analysis (TG-DTA) as well as pHzpc analyses. The results suggested that the interactions between the co-solvent and the Mg/Al-HT affected the nucleation, resulting in the variation of crystallinity. The employment of glycerin co-solvents during the nucleation was conducive to the combination of crystal water with the brucite sheets. The hydrotalcite (mix-MHT) obtained by adding glycerin co-solvent during the nucleation possessed the smallest particle sizes with the narrowest size distribution and the most hydrophobic particle surfaces, which made the mix-MHT particles disperse uniformly throughout the PP matrix due to their good compatibility with PP. The improvement of the compatibility between the particles and the polymer was mainly caused by the decrease of the hydrophilicity on the surface of the particles due to the presence of glycerin in the interlayer spaces of the mix-MHT particles. The insertion of the mix-MHT particles into the PP matrix could also significantly enhance the thermal stability and maintain the mechanical properties of PP, and the mix-MHT had the best performance as a flame retardant with the PP matrix.

Microwave-assisted preparation of SO42− intercalated hydrotalcites for ammonia–nitrogen removal

The intercalation of SO42− into MgAl hydrotalcites was investigated under microwave irradiation, and the structural and physiochemical properties of the SO42− intercalated hydrotalcites were determined using XRD, FTIR, SEM/EDS, BET and BJH techniques. Microwave irradiation contributed to the intercalation of SO42− anions, which brought about high amounts of SO42− into the interlayer spaces and high crystallinity. The intercalation of SO42− enhanced the acidic sites that cooperated with alkaline sites to activate the NH4+ molecules simultaneously leading to a significant increase in the removal of ammonia–nitrogen in synthetic wastewater. Kinetics and thermodynamics of the SO42− intercalation under microwave irradiation revealed that Langmuir isotherm fitted the experimental results well, and the kinetics were more accurately represented by a pseudo second-order model. The intercalation–reconstruction process was chemisorption nature mainly through hydrogen bond forces, followed the exchange of interlayer –OH anions and SO42−.

Preparation of Ti species coating hydrotalcite by chemical vapor deposition for photodegradation of azo dye

TiO2 in anatase crystal phase is a very effective catalyst in the photocatalytic oxidation of organic compounds in water. To improve its photocatalytic activity, the Ti-coating MgAl hydrotalcite (Ti-MgAl-LDH) was prepared by chemical vapor deposition (CVD) method. Response surface method (RSM) was employed to evaluate the effect of Ti species coating parameters on the photocatalytic activity, which was found to be affected by the furnace temperature, N2 flow rate and influx time of precursor gas. Application of RSM successfully increased the photocatalytic efficiency of the Ti-MgAl-LDH in methylene blue photodegradation under UV irradiation, leading to improved economy of the process. According to the results from X-ray diffraction, scanning electron microscopy, Brunner-Emmet-Teller and Barrett-Joyner-Hallender, thermogravimetric and differential thermal analysis, UV-vis diffuse reflectance spectra analyses, the Ti species (TiO2 or/and Ti4+) were successfully coated on the MgAl-LDH matrix. The Ti species on the surface of the Ti-MgAl-LDH lead to a higher photocatalytic performance than commercial TiO2-P25. The results suggested that CVD method provided a new approach for the industrial preparation of Ti-coating MgAl-LDH material with good photocatalytic performances.

Facile Hydrothermal Preparation of Carboxymethyl Chitosan Functionalized Hydrotalcite Composite with Enhanced Adsorption Capacity for Cu(II) Ions

In order to enhance the adsorption capacity of hydrotalcite material for heavy metal ions, the LDH/CMC composite was prepared by a simple hydrothermal method. The XRD pattern showed that the presence of CMC has no obvious influence on the crystal structure of hydrotalcites. The FT-IR and UV-vis DRS analyses showed that the CMC functionalized surface has been obtained. The SEM and BET/BJH showed that the morphologies, textural and surface chemical properties of LDH were affected remarkably after the introduction of CMC. The weight percentage of CMC in the LDH/CMC composite was estimated to be about 17.4%. The adsorption experiments showed the LDH/CMC composite exhibited high efficiency in the Cu(II) removal at pH > 6.5, affording Cu(II) removal rates of 92.3%. The results demonstrated that the LDH/CMC composite was a suitable adsorbent for Cu(II)-contaminated wastewater treatment.

Optimization of ammonia nitrogen removal by SO42− intercalated hydrotalcite using response surface methodology

SO42− intercalated Mg–Al hydrotalcite (S-LDH) was prepared under microwave irradiation and characterized by powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The S-LDH had a typical layered structure containing SO42− anions, and intercalation of SO42− into the interlayer spaces caused reduction of crystallinity and crystal sizes compared to the Mg–Al hydrotalcite precursor. Furthermore, the Box–Behnken design, an experimental design for response surface methodology (RSM), was used to study the NH3–N removal by S-LDH under microwave irradiation. The parameters including S-LDH amount, irradiation time, temperature and initial pH were optimized by RSM. From the analysis of variance, it was found that RSM could be used effectively to model and improve the NH3–N removal efficiency. The optimum conditions were 1.0 g L−1 of the S-LDH, 9.0 min, 70 °C and initial pH 10.0 to achieve 90.4% of the NH3–N removal rate. Overall, the S-LDH showed a high performance under moderate operating conditions for NH3–N removal.