Xinjian Jia

New fluorine-doped H2(H2O)Nb2O6 photocatalyst for the degradation of organic dyes

A new solid niobic acid phase, H2(H2O)Nb2O6, with fluorine (F) doping was crystallized using hydrothermal chemistry. F-doped H2(H2O)Nb2O6 octahedra could function as an efficient heterogeneous catalyst for the photodegradation of organic pollutants in water under UV light irradiation. The high photocatalytic activity of the F-doped H2(H2O)Nb2O6 materials is attributed to a synergistic effect of the specific surface area, the surface characteristics and the crystal structure. Our results suggest novel ways of controlling the crystallization of niobium oxides, further the fundamental understanding of their structure–property relationships, and may lead to their application in fields such as environmental protection and energy production.

Bouquet-like calcium sulfate dihydrate: a highly efficient adsorbent for Congo red dye

A unique bouquet-like calcium sulfate dihydrate (BCSD) was successfully synthesized from calcium chloride and aluminum potassium sulfate in aqueous sodium carboxymethyl cellulose (CMC) solution by means of a metathesis reaction. The morphology and structure of BCSD were characterized by scanning electron microscopy, powder X-ray diffraction and transmission electron microscopy. The adsorption of different organic dyes from aqueous solutions onto the as-synthesized BCSD was then investigated, taking into account the influences of adsorbent dose (1.0–3.5 g L−1), solution pH (5.0–12.0) and adsorption time. The results indicated that the temperature and agitation rate had no effect on the morphology of the samples. With the increase of CMC concentration from 0.10% to 0.50%, lamellar calcium sulfate dihydrate (LCSD) gradually transformed into rod-like calcium sulfate dihydrate (RCSD), and eventually generated BCSD. The as-prepared BCSD was monoclinic with preferential [021] and [041] orientations. Moreover, BCSD selectively adsorbed Congo red (CR) instead of rhodamine B and methyl orange. The adsorption equilibrium process of CR was an exothermic process and could adequately be described by the Langmuir isotherm model. The calculated maximum adsorption quantity (qmax) was 1224.09 mg g−1 at 303.5 K, which was almost 12 times larger than that onto LCSD (100.80 mg g−1). Additionally, the adsorption process of CR was a multi-step process, and the adsorption kinetics could be described in terms of a pseudo-second-order model. From attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy studies it was concluded that CR was chemisorbed on BCSD. These results indicate that BCSD is a promising candidate in wastewater treatment.

A thermo-sensitive supramolecular hydrogel derived from an onium salt with solution–gel–crystal transition properties

The gelation ability of melamine was evaluated under various acidic conditions, and the related gelator aggregates were investigated with scanning electron microscopy, transmission electron microscopy, single-crystal X-ray diffraction, thermo-gravimetric analysis, differential scanning calorimetric analysis, rheological experiments, 1H nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy and powder X-ray diffraction. It was found that melamine interacted strongly with a number of organic/inorganic acids in water, forming thermal-reversible supramolecular hydrogels with different critical gelator concentrations (CGCs). The CGCs of gelators successively made with salicylic acid, m-hydroxybenzoic acid and p-hydroxybenzoic acid decreased because of the steric hindrance, whereas those related to oxalic acid dihydrate and orthoboric acid presented higher values due to the lack of a phenyl ring in the molecular structures. More interestingly, a unique onium salt, 2,4,6-triamino-1,3,5-triazin-1-ium benzoate dihydrate (TTIBD), was formed via the Lewis acid–base reaction of benzoic acid and melamine. It crystallized in the monoclinic space group C2/c (Z = 8) with lattice parameters a = 21.477 (3) A, b = 10.2253 (14) A, c = 12.3312 (17) A and β = 98.717 (3)°. The formed hydrogel not only exhibited thermo-sensitive characteristics and solid-like behavior, but also showed a solution–gel–crystal transition, being an amorphous-to-crystalline phase transition. By increasing the concentration from 0.04 to 0.12 mol L−1, the gel–solution transition temperature increased from 23.0 to 49.5 °C, and the gel–crystal transition time decreased from 430 to 253 min, but both leveled off upon increasing the concentration. The TTIBD crystal along with the corresponding hydrogel was self-assembled via hydrogen bonds and π–π stacking interactions.