Yao Jun Zhang

A new alkali-activated steel slag-based cementitious material for photocatalytic degradation of organic pollutant from waste water

A new type of Ni,Ca-cementitious material was firstly synthesized via a two-step reaction of alkali-activated steel slag polymerization and ion exchange. The XRF results showed that almost all the Na(+) ions in the matrix of Na,Ca-cementitious material were replaced by Ni(2+) ions at room temperature. The new hydrated products of metahalloysite (Si(2)Al(2)O(5)(OH)(4)) and calcium silicate hydrate (CSH) were formed in the Na,Ca-cementitious material. The diffuse reflectance UV-vis near infrared ray spectrum was blue-shifted due to the strong interaction between Ni(2+) and negative charge of [AlO(4)](5-) tetrahedron in the framework of cementitious material. The Ni,Ca-cementitious material was used as a catalyst for the photocatalytic degradation of methylene blue dye and showed a degradation rate of 94.39% under UV irradiation. The high photocatalytic degradation activity was suggested to be the synergistic effect of the cementitious matrix, Ni(2+) ions and the iron oxides of wustite (FeO) and calcium iron oxide (Ca(2)Fe(2)O(5)) from the steel slag. A probable mechanism of photocatalytic oxidative degradation was proposed.

A novel V-doped CeO2 loaded alkali-activated steel slag-based nanocomposite for photocatalytic degradation of malachite green

abstract In the present study, V-doped CeO2 loaded alkali-activated steel slag-based nanocomposite (V-CeO2-ASSN) as a novel catalyst for photocatalytic degradation of malachite green dye was firstly reported. X-ray diffraction (XRD) results demonstrated that there were mainly mineral phase of calcium silicate hydrate (CSH) and lawsonite, (CaAl2Si2O7(OH)2·H2O) in the alkali-activated steel slag-based nanocomposites, and CeO2 crystallite size is close to 20 nm dispersed on the surface of ASSN. The photocatalystic activity of vanadium doped CeO2 loaded alkali-activated steel slag-based nanocomposite catalyst showed high degradation efficiency of malachite green (MG) dye under ultraviolet light irradiation, and the highest degradation rate can reach 100%. The photocatalytic degradation belongs to the first-order reaction kinetics.

Geopolymer Microstructure and Hydration Mechanism of Alkali-Activated Fly Ash-Based Geopolymer

The microstructure and hydration mechanism of alkali-activated fly ash-based geopolymer were studied by means of scanning electron microscope (SEM) coupled with energy dispersive X-ray analysis (EDXA) and field emission scanning electron microscope (FESEM). The FESEM photomicrographs indicted that the fly ash-based geopolymer showed three dimensional frameworks with an average particle size of 50 nm. EDXA results demonstrated that the Na-PSS type geopolymer was produced via the disintegration of Si-O-Al and Si-O-Si chemical bonds and the polycondensation reaction between [SiO4]4-and [AlO4]5- tetrahedrons in spherical fly ash particles under alkaline condition.

A new In2O3 and NiO co-loaded fly ash-based nanostructural geopolymer for photocatalytic H2 evolution

ABSTRACT A nanostructural alkali-activated fly ash-based geopolymer (AFAG) by co-loaded bimetallic oxide semiconductors of In2O3 and NiO were firstly synthesized and used as an excellent nanocatalyst for production of hydrogen by water splitting. XRD results revealed that In2O3 with average particle size of about 14 nm and NiO in the form of amorphous phase dispersed on the surface of AFAG support. UV-vis DRS and photoluminescence spectra showed that the 5In2O3-NiO/AFAG sample has the widest response to sunlight spectrum and the weakest photoluminescence spectrum, respectively. The 5In2O3-NiO/AFAG sample exhibits the excellent photocatalytic activity of H2 evolution of 3180 µmol/g under the irradiation of solar simulation source for 6 h due to its mesoporous structure coupled with In2O3 and NiO.

A new graphene/geopolymer nanocomposite for degradation of dye wastewater

ABSTRACT A novel graphene/geopolymer nanocomposite was firstly synthesized by using two-dimension graphene (GR) and alkali-activated granulated blast furnace slag-based geopolymer (ASG), and used to degrade simulation dye effluents. Diffuse reflectance UV–Vis spectrum indicated that the maximum absorption wavelength of the nanocomposite (GR/ASG) is red-shift to the visible region. The pore diameter distribution results of the GR/ASG1 sample showed that at least 89.59% of pore volume centralized on the region of 2–50 nm. The photocatalytic degradation efficiencies of samples for methyl violet dye is in the order of GR/ASG1 > GR/ASG2 > ASG under the irradiation of UV. The GR/ASG1 photocatalyst exhibited the highest degradation efficiency and approached to 91.16% for 110 min. The photocatalytic degradation reaction belongs to the second-order reaction kinetics.

Microstructure of Alkali-Activated Granulated Blast Furnace Slag-Based Geopolymer

The microstructure of alkali-activated granulated blast furnace slag-based geopolymer was studied by means of field emission scanning electron microscope (FESEM) coupled with energy dispersive X-ray analysis (EDXA). FESEM images showed that the geopolymer material has worm-like microstructure in the nanoscale with an average particle size of 20 nm. EDXA results demonstrated that the Na-based and Ca-based geopolymers were produced via the disintegration of amorphous phases and some minerals in GBFS and polycondensation reaction of oxygen-silicon and oxygen-aluminum tetrahedrons under alkaline condition.

Synthesis of eco-friendly CaWO4/CSH nanocomposite and photocatalytic degradation of dyeing pollutant

ABSTRACT A new type of eco-friendly CaWO4/CSH (calcium silicate hydrate) nanocomposite was firstly synthesized by the reaction of ammonium metatungstate and alkali-activated granulated blast furnace slag-based gelled material. The XRD and FESEM results showed that the CaWO4/CSH nanocomposite was composed of CaWO4 crystal phase and calcium silicate hydrate (CSH). The pore size distribution result indicated that the 5CaWO4/CSH nanocomposite held the highest mesopore volume percentage of 94.17%. The 5CaWO4/CSH nanocomposite exhibited the highest degradation rate of 90.29%. The photocatalytic degradation reaction of basic violet 5BN dye belonged to the second-order reaction kinetics. The excellent photocatalytic activity of 5CaWO4/CSH nanocomposite was attributed to the synergistic effect of the active phase of CaWO4 and the mesopore structure of CSH.

Photocatalytic degradation of malachite green by a novel CeO2 loaded alkali-activated steel slag-based nanocomposite

ABSTRACT A new CeO2 loaded alkali-activated steel slag-based nanocomposite (CeO2-ASSN) for photocatalytic degradation of malachite green dye was firstly synthetized via incipient wetness impregnation method. The XRD and SEM results indicated that calcium silicate hydrate (CSH) was mainly mineral phase in the alkali-activated steel slag-based nanocomposite specimens, and the loaded CeO2 particles with particle size about 15 nm were highly dispersed on the surface of photocatalyst carrier. Photoluminescence intensity of the CeO2 loaded specimens was obviously decreased and the 8wt% CeO2 loaded nanocomposite specimen showed the weakest photoluminescence intensity. The CeO2 loaded specimens exhibited high photocatalytic degradation efficiency of malachite green dye under UV light irradiation for 80 min, and the maximum degradation rate of the 8wt% CeO2 loaded nanocomposite specimen could reach 100%. It was ascribed to the co-action of CeO2 active component and FeO in the carrier. The formation of the coupled semiconductors could promote the high efficiency separation of the photogenerated electron-hole pairs. The photocatalytic degradation belongs to the first-order reaction kinetics.

Alkali-Activated Steel Slag-Based Mesoporous Material as a New Photocatalyst for Degradation of Dye from Wastewater

A new photocatalyst for degradation of dye from waste-water using alkali-activated steel slag-based mesoporous material (ASSMM) by adding pore-forming agent was firstly prepared. The XRD results showed that there were mainly mineral phase of calcium silicate hydrate (CSH) and lawsonite, (CaAl2Si2O7(OH)2·H2O) in the ASSMM samples by adding of pore-forming agent. The result of BET specific surface area indicated that more than 85% of pore volume principally centralized on mesoporous range with the pore size diameter of 2-50nm for the sample (0.1ASSMM) by adding of 0.1 wt% pore-forming agent. The degradation rate of malachite green (MG) dye is in the order of 0.1ASSMM > 5ASSMM > 1ASSMM > ASSMM > dye of direct photolysis. The 0.1ASSMM photocatalyst exhibited the highest degradation rate under UV irradiation, and the highest degradation rate can reach 95.53%. The photodegradation belongs to the first-order reaction kinetics.

Study on Performance of Alkali-Activated Flyash-Based Geopolymer Reinforced by Silica Fume and Styrene-Acrylic Emulsion

In order to improve the inherent fragility of alkali-activated fly ash-based geopolymer, the silica fume and styrene-acrylic emulsion were used to reinforce and toughen the geopolymer. The phase structure, morphology and chemical composition were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray fluorescence (XRF). The results showed that the mechanical properties of alkali-activated fly ash-based geopolymer were dramaticlly improved and the specimen with doping content of 10 wt% silica fume, 1wt% styrene-acrylic emulsion and 15wt% the alkaline excitation agent Na2SiO39H2O showed the highest compressive and flexural strengths of 42.11MPa and 5.30MPa in the ambient temperature curing 28d, respectively. SEM results indicated that doped silica fume and styrene-acrylic emulsion were embedded within the matrix of fly ash-based geopolymer. XRD results demonstrated that the mineral structures did not change obviously when silica fume and styrene-acrylic emulsion were added to the geopolymer