Xiaoman He

Precursor preparation of Zn–Al layered double hydroxide by ball milling for enhancing adsorption and photocatalytic decoloration of methyl orange

An amorphous photocatalyst was prepared via simple dry milling of Zn basic carbonate (Zn4CO3(OH)6·H2O) and Al hydroxide (Al(OH)3) as a precursor of Zn–Al layered double hydroxide (LDH) and the precursor was agitated in water to simply synthesize the Zn–Al LDH for comparison. The adsorption and photocatalytic activity of the Zn–Al LDH and the precursor were studied via the removal of methyl orange (MO) and decoloration of MO under ultraviolet light irradiation in aqueous solution, respectively. The precursor exhibits much higher decoloration efficiency towards MO than the Zn–Al LDH product because of the synergistic effect of the intercalation reaction and its photocatalytic activity. The amorphous precursor could easily incorporate MO molecules to form MO intercalated LDH, allowing easy access of the organic pollutant to the photocatalyst sample, resulting in an obvious improvement in photocatalytic performance. The novel idea to use the precursor sample instead of the synthesized final product may be applied in other fields to increase the required performances.

Simultaneous synthesis of ettringite and absorbate incorporation by aqueous agitation of a mechanochemically prepared precursor

Co-grinding of calcium hydroxide, aluminum hydroxide and gypsum was performed to prepare an activated precursor for synthesizing ettringite (simple formula 3CaO·Al2O3·3CaSO4·32H2O). Agitation of the precursor in an aqueous solution with a target absorbate, even at room temperature, allowed not only the synthesis of ettringite, but also absorbate incorporation at stoichiometric amounts accompanying the synthesis reaction. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric differential thermal analyses (TG-DSC) were conducted to characterize the precursors and synthesized products. Potassium phosphate was used as the target absorbate to evaluate possible incorporation of both sulphate and phosphate coexisting in the ettringite structure. This confirmed that the novel idea of incorporating pollution components in a reaction may allow for removing efficiencies that are much higher than obtainable from traditional sorption operation.

Decomposition pathways of polytetrafluoroethylene by co-grinding with strontium/calcium oxides

ABSTRACT Waste polytetrafluoroethylene (PTFE) could be easily decomposed by co-grinding with inorganic additive such as strontium oxide (SrO), strontium peroxide (SrO2) and calcium oxide (CaO) by using a planetary ball mill, in which the fluorine was transformed into nontoxic inorganic fluoride salts such as strontium fluoride (SrF2) or calcium fluoride (CaF2). Depending on the kind of additive as well as the added molar ratio, however, the reaction mechanism of the decomposition was found to change, with different compositions of carbon compounds formed. CO gas, the mixture of strontium carbonate (SrCO3) and carbon, only SrCO3 were obtained as reaction products respectively with equimolar SrO, excess SrO and excess SrO2 to the monomer unit CF2 of PTFE were used. Excess amount of CaO was needed to effectively decompose PTFE because of its lower reactivity compared with strontium oxide, but it promised practical applications due to its low cost.

Enhanced phosphate removal from wastewater by using in situ generated fresh trivalent Fe composition through the interaction of Fe(II) on CaCO 3

Excessive existences of nutrients such as phosphate in the aqueous environment remain as a heavy concern although many researches have been reported for dealing with their removal. Based on the understanding toward the interactions of Fe compounds with phosphate and carbonate from many available researches, we designed a very simple and efficient approach for phosphate removal by using in situ generated fresh trivalent Fe composition through the interaction of Fe(II) as FeSO4 on CaCO3. Addition and agitation of Fe(II) and CaCO3 simultaneously to phosphate solution allowed an amorphous Fe(III)-P or Ca-Fe(III)-P precipitation, with a phosphate removal rate close to 100%, to reduce the residual phosphorus concentration less than 0.03 mg/L from 100 mg/L, reaching the discharge limit, even with the addition amounts of CaCO3 as low as a stoichiometric ratio of CaCO3/PO43- at 0.9 and ratio of Fe(II)/PO43- at 1.5, and the percent of P2O5 in the precipitate was as high as 19.4% enough as phosphate source for fertilizer production. Different from the alkaline process with enough OH- group, the slow hydrolysis of CaCO3 resulting in low concentration of OH- group for the formation of Fe(OH)2, which was oxidized soon by air into trivalent Fe, achieved a continuous generation of fresh ferric composition for phosphate precipitation and could avoid its rapid formation and subsequent transformation into stable FeOOH of large particle size to lose the activity. These results based on the synergistic effect of using CaCO3 and Fe(II) together may have applications in the treatment of eutrophic wastewater through a process with many advantages of easy operation and low-cost besides the high removal efficiency with phosphate percentage inside the precipitate high enough to serve for fertilizer production.