Hao Ding

Enhanced photochemical oxidation ability of carbon nitride by π–π stacking interactions with graphene

Abstract A one-pot method for the preparation of g-C 3 N 4 /reduced graphene oxide (rGO) composite photocatalysts with controllable band structures is presented. The photocatalysts are characterized by Fouirer transform infrared spectroscopy, X-ray diffraction, scanning electron microscope, transmission electron microscope, and Mott-Schottky analysis. The valance band (VB) of g-C 3 N 4 exhibits a noticeable positive shift upon hybridizing with rGO, and thus results in a strong photo-oxidation ability. The g-C 3 N 4 /rGO composites show a higher photodegradation activity for 2,4-dichlorophenol (2,4-DCP) and rhodamine B (RhB) under visible light irradiation (λ ≥ 420 nm). The g-C 3 N 4 /rGO-1 sample exhibits the highest photocatalytic activity, which is 1.49 and 1.52 times higher than that of bulk g-C 3 N 4 for 2,4-DCP and 1.52 times degradation, respectively. The enhanced photocatalytic activity for g-C 3 N 4 originates from the improved visible light usage, enhanced electronic conductivity and photo-oxidation ability by the formed strong π–π stacking interactions with rGO.

Influence of phase structure and morphology on the photocatalytic activity of bismuth molybdates

Bismuth molybdate photocatalysts with different phase structures and morphologies were controllably synthesized via a refluxing method by adjusting the pH in the reaction system. Bi2MoO6 nanosheets were easily obtained under acidic conditions, while Bi3.64Mo0.36O6.55 nanoparticles were formed in circumneutral and basic solutions. The mechanism for the formation and phase transition of these two bismuth molybdates is based on tuning the pH value, which can control the growth rate along different crystal axes and the formation of different hydrolysis products that act as the initial seeds of the crystallographic phases. The photocatalytic activity of the Bi2MoO6 nanosheets for MB and MO degradation was higher than that of the Bi3.64Mo0.36O6.55 nanoparticles under visible light irradiation, and the highest photocatalytic activity was observed for the Bi2MoO6 nanosheets prepared at pH 6.0. The high visible-light photocatalytic activity of the Bi2MoO6 nanosheets arises from the easy separation and transfer of photogenerated electron–holes in the nanosheet’s structure as well as the narrow band gap, which leads to an improvement in the visible absorption ability. Electron spin resonance (ESR) and a photogenerated carrier trapping experiment suggested that both Bi2MoO6 and Bi3.64Mo0.36O6.55 had the same photocatalytic mechanism and the main oxidative species for these samples was the hydroxyl radical.

Preparation of black-pearl reduced graphene oxide–sodium alginate hydrogel microspheres for adsorbing organic pollutants

The black-pearl reduced graphene oxide-sodium alginate (rGO-SA) hydrogel microspheres are prepared by the external emulsification and thermal reduction method, which are characterized by scanning electron microscope (SEM) and X-ray Diffraction (XRD). Sodium alginate (SA) serves as a template to form a 3D porous network structure, which can prevent the agglomeration and restacking of rGO sheets efficiently. The size of hydrogel microsphere can be controlled by adjusting the size of the liquid drop. The effects of rGO content (wt%), contact time, initial concentration of phenol, adsorption temperature and adsorption dose on the adsorption capacity of rGO-SA microspheres are investigated. The kinetics and isotherm data are well described by the pseudo-second-order kinetic model and the Langmuir equation, respectively. Thermodynamic results demonstrate the spontaneous and endothermic nature of adsorption. This rGO-SA microsphere exhibits the favorable adsorption performance for phenol, BPA and tetracycline. The rGO-SA microsphere might be a potential candidate for efficient adsorbents in water treatment.

Preparation and Characterization of ZnO Nanoparticles Supported on Amorphous SiO2

In order to reduce the primary particle size of zinc oxide (ZnO) and eliminate the agglomeration phenomenon to form a monodisperse state, Zn2+ was loaded on the surface of amorphous silica (SiO2) by the hydrogen bond association between hydroxyl groups in the hydrothermal process. After calcining the precursors, dehydration condensation among hydroxyl groups occurred and ZnO nanoparticles supported on amorphous SiO2 (ZnO–SiO2) were prepared. Furthermore, the SEM and TEM observations showed that ZnO nanoparticles with a particle size of 3–8 nm were uniformly and dispersedly loaded on the surface of amorphous SiO2. Compared with pure ZnO, ZnO–SiO2 showed a much better antibacterial performance in the minimum inhibitory concentration (MIC) test and the antibacterial properties of the paint adding ZnO–SiO2 composite.

Mechanical Grinding Preparation and Characterization of TiO2-Coated Wollastonite Composite Pigments

TiO2-coated wollastonite composite pigments were prepared by the mechano-chemical grinding of wollastonite and TiO2 powder together in a wet ultrafine stirred mill. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and infrared spectra were used to investigate the microstructures and morphologies of the composite and the reaction mechanism. The results indicate that the TiO2-coated wollastonite composite pigments have similar properties to titanium dioxide pigment, showing much better properties than dry and wet mixing of wollastonite and TiO2. The hiding power of TiO2-coated wollastonite composite pigments (45% TiO2) is 17.97 g/m2, reaching 81.08% of titanium dioxide. A firm combination between wollastonite and TiO2 is obtained through a surface dehydroxylation reaction during the mechano-chemical method.

Microstructural Modification and Characterization of Sericite

Activated sericite was prepared by thermal modification, acid activation and sodium modification, and it was characterized by X-ray diffraction (XRD) analysis, differential scanning calorimetry (DSC), N2 adsorption test, thermo-gravimetric analysis (TGA), nuclear magnetic resonance (NMR), and scanning electron microscope (SEM). The results indicated that the crystallinity of raw sericite decreased after thermal modification; the pores with sizes between 5 nm to 10 nm of thermal-modified sericite have collapsed and the surface area increased after thermal modification. The dissolving-out amount of Al3+ reached ca. 31 mg/g in the optimal processing conditions during acid activation; cation exchange capacity (CEC) of acid-treated sericite increased to 56.37 mmol/100 g meq/g after sodium modification compared with that of raw sericite (7.42 mmol/100 g). The activated sericite is a promising matrix for clay-polymer nanocomposites.

Preparation of CaCO3-TiO2 Composite Particles and Their Pigment Properties

CaCO3-TiO2 composite particles were prepared with calcium carbonate (CaCO3) and TiO2 in stirred mill according the wet grinding method. The pigment properties, morphology, and structure of CaCO3-TiO2 composite particles and the interaction behaviors between CaCO3 and TiO2 particles were explored. In the CaCO3-TiO2 composite particles, TiO2 is uniformly coated on the surface of CaCO3 and the firm combination between CaCO3 and TiO2 particles is induced by the dehydration reaction of surface hydroxyl groups. CaCO3-TiO2 composite particles have similar pigment properties to pure TiO2. The hiding power, oil absorption, whiteness and ultraviolet light absorption of composite particles are close to those of pure TiO2. The application performance of CaCO3-TiO2 composite particles in the paint is consonant with their pigment properties. The contrast ratio of the exterior paint containing CaCO3-TiO2 composite particles is equivalent to that of the paint containing the same proportion of pure TiO2.

Preparation of TiO 2 -coated barite composite pigments by the hydrophobic aggregation method and their structure and properties

We obtained hydrophobic barite (BaSO4) and rutile titanium dioxide (TiO2) particles (as raw materials) by organic surface modification. Subsequently, TiO2-coated barite composite pigments were prepared via the hydrophobic aggregation of heterogeneous particles in a water medium. The pigment properties of the TiO2-coated barite composite pigments were characterized and evaluated by determining their hiding power, oil absorption value and whiteness. The optical properties were determined by obtaining their UV-vis diffuse reflectance spectra and using the CIE-L*a*b* method. The morphology and bonding properties were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (IR). The results show the similarity between the composite pigment and pure rutile TiO2: when the mass ratio of rutile TiO2 in the composite pigment was 60%, the hiding power of the TiO2-coated barite composite pigment was 90.81% of that of pure rutile TiO2. Moreover, the surfaces of the barite particles were uniformly and firmly coated by TiO2, with a hydrophobic association occurring between the hydrophobic carbon chains on the surfaces of barite and TiO2 particles.

Preparation of Nano-TiO2-Coated SiO2 Microsphere Composite Material and Evaluation of Its Self-Cleaning Property

In order to improve the dispersion of nano-TiO2 particles and enhance its self-cleaning properties, including photocatalytic degradation of pollutants and surface hydrophilicity, we prepared nano-TiO2-coated SiO2 microsphere composite self-cleaning materials (SiO2–TiO2) by co-grinding SiO2 microspheres and TiO2 soliquid and calcining the ground product. The structure, morphology, and self-cleaning properties of the SiO2–TiO2 were characterized. The characterization results showed that the degradation efficiency of methyl orange by SiO2–TiO2 was 97%, which was significantly higher than that obtained by pure nano-TiO2. The minimum water contact angle of SiO2–TiO2 was 8°, indicating strong hydrophilicity and the good self-cleaning effect. The as-prepared SiO2–TiO2 was characterized by the nano-TiO2 particles uniformly coated on the SiO2 microspheres and distributed in the gap among the microspheres. The nano-TiO2 particles were in an anatase phase with the particle size of 15–20 nm. The nano-TiO2 particles were combined with SiO2 microspheres via the dehydroxylation of hydroxyl groups on their surfaces.

The modification and characterization of thermal-treated sericite by fluorosilicate

In this article, the thermal-treated sericite was modified by both fluorosilicate and the combination of fluorosilicate and nitric acid in order to reduce its layer charge and gain cation exchange capabilities for the preparation of sericite/polymer nanocomposites. After several orthogonal experiments and single factor experiments, the optimal experimental conditions were set up and we found that the combination of nitric acid and fluorosilicate is much more effective than fluorosilicate alone. Chemical composition analysis showed Al3+ was dissolved out from sericite and the dissolving amount is 65 mg/g under optimal experimental conditions. Combining the NMR test, it is considered that the Si/Al ratio in the tetrasheet of the modified product increased from 3.48 to 10. The layer charge reduced and the CEC value increased after fluorosilicate modification, which means the modified sericite is a promising matrix for clay-polymer nanocomposites.