An extract of the indigenous plant jack bean (Canavalia ensiformis) was used to produce calcite, an effective biomaterial. The formation of calcite using this extract was compared, under stable conditions, to that using commercially available purified urease. Xray diffraction and scanning electron microscopy were employed to elucidate the mechanism of calcite formation from the crude plant extracts. The results revealed that urease in the jack bean crude extracts catalyzed the hydrolysis of urea in liquid-state cultures. The procedure described herein is a simple and useful method of calcite mineral precipitation that does not require cultivation of microorganisms or further purification of crude extracts. This study suggests that crude extracts of Canavalia ensiformis have the potential to be used in place of purified forms of urease during remediation of cracks and to increase the strength of materials.

The setting behavior of geopolymers is affected by the type of source materials, alkali activators, mix formulations, and curing conditions. Calcium hydroxide is known to be an effective additive to shorten the setting period of geopolymers. However, there is still room for improvement in the understanding of the effect of calcium hydroxide on the setting and phase evolution of geopolymers. In this study, the setting behavior and phase evolution of geopolymer containing calcium hydroxide were investigated by XRD analysis. The setting time of the geopolymer was inconsistently shortened as the amount of calcium hydroxide increased. A low calcium hydroxide dose of up to 2% of the total mix weight could contribute to the enhancement of compressive strength of geopolymers besides a fast-setting effect. The C-S-H gel is rapidly precipitated at the early stage of reaction in geopolymers containing high calcium hydroxide with some of the calcium hydroxide remaining intact. The ex-situ high-temperature XRD analysis and Rietveld refinement results revealed that geopolymer and C-S-H gel transformed into Si-rich nepheline and wollastonite, respectively. The wollastonite was also observed in heat-treated geopolymers with a low calcium hydroxide dose. It is believed that C-S-H gel can be precipitated along with geopolymers regardless of how much calcium hydroxide is added.

There is no standardized procedure for producing geopolymers; therefore, many researchers develop their own procedures for mixing and curing to achieve good workability and strength development. The curing scheme adopted is important in achieving maximum performance of resultant geopolymers. In this study, we evaluated the impact of sealed and unsealed curing on mechanical strength of geopolymers. Fly ash-based geopolymers cured in sealed and unsealed moulds clearly revealed that retention of water during curing resulted in superior strength development. The average compressive strength of sealed-cured geopolymers measured after 1 day of curing was a modest 50 MPa, while after 7 day curing the average compressive strength increased to 120~135 MPa. In the unsealed specimens the average compressive strength of geopolymers was lower; ranging from 60 to 90 MPa with a slight increase as the curing period increased. Microcracking caused by dehydration is postulated to cause the strength decrease in the unsealed cured samples. These results show that water is a crucial component for the evolution of high strength three-dimensional cross-linked networks in geopolymers.

Zirconia-carbon (ZC) composites were prepared via calcination of Zr-based metal organic frameworks, UiO-66 and amino-functionalized UiO-66, under N₂ atmosphere. The prepared composites were characterized using a series of instrumental analyses. The surface area of the ZC composites increased with the increase of calcination temperature, with the formation of a graphite oxide phase observed at 900 °C. The composites were used for adsorptive removal of a dye (crystal violet, CV) and a pharmaceutical and personal care product (salicylic acid, SA). The increase of the calcination temperature resulted in enhanced adsorption capability of the composites toward CV. The composite calcined at 900 °C exhibited a maximum uptake of 243 mg·g⁻¹, which was much greater than that by a commercial activated carbon. The composite was also effective in SA adsorption (102 mg·g⁻¹), and N-functionalization of the composite further enhanced its adsorption capability (109 mg·g⁻¹). CV adsorption was weakly influenced by solution pH, but was more dependent on the surface area and pore volume of the ZC composite. Meanwhile, SA adsorption showed strong pH dependence, which implies an active role of electrostatic interactions in the adsorption process. Base-base repulsion and hydrogen bonding are also suggested to influence the adsorption of CV and SA, especially for the N-functionalized composite.

The present study investigated fluorene biodegradation by Sphingobacterium sp. KM-02 in the presence of heavy metals. A fluorene-degrading strain of Sphingobacterium was isolated from polycyclic aromatic hydrocarbon-contaminated soil near a mine-impacted area in Korea. When Sphingobacterium sp. KM-02 was grown in a medium with fluorene as the sole carbon source, it removed 78.4% of this compound within 120 h. Identification of the metabolic intermediates (9-fluorenone, 4-hydroxy-9-fluorenone, and 8-hydroxy-3,4-benzocoumarin) were also performed. Composting experiments under laboratory conditions indicated that this microbe also removed fluorene from contaminated soil. In particular, treatment of microcosm soil with strain KM-02 for 20 days resulted in a 65.6% reduction of fluorene concentration. Experiments of effects of heavy metals on fluorene removal by strain KM-02 showed that 10 mg/L cadmium, copper, zinc, and lead, reduced growth and fluorene degradation by this microbe. Cadmium and copper had strong effects at 10 mg/L, although zinc and lead had relatively slight inhibitory effect at concentrations of 10 and 100 mg/L. Arsenic had no effect on the growth or fluorene degradation, even at 100 mg/L.