Guangyan Tian

From nanorods of palygorskite to nanosheets of smectite via a one-step hydrothermal process

The structural evolution of silicate opens a new avenue to cognize its microstructure, intensify its properties and extend its application. Herein, the one-step transformation of palygorskite (PAL) nanorods into smectite nanosheets was successfully achieved under mild hydrothermal condition with no addition of any extra chemicals. The structural evolution of PAL at different reaction stages and the change in physico-chemical characteristics was intensively studied through field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetry (TG) and Fourier transform infrared spectroscopy (FTIR) techniques. The key factors determining the transformation process were clarified. It was found that the moderate mechanical grinding, pH values and the existence of dolomite are essential to realize the transformation, and alkaline condition may facilitate the transformation. The transformation from nanorods to nanosheets is a rebuilding process of crystals, and the c/2 slide of tetrahedrons represents the main transformation mechanism. After the hydrothermal process, the adsorption capability of RPAL for Cu(II) evidently enhanced by 167%, and 99.01% of Cu(II) ions (only 64.9% for raw PAL) can be removed from 20 mg L−1 of Cu(II) solution.

Attapulgite Modified with Silane Coupling Agent for Phosphorus Adsorption and Deep Bleaching of Refined Palm Oil

Attapulgite (ATP) clay was modified with different silane coupling agents [3-triethoxysilylpropylamine (KH550), γ-glycidoxypropyltrimethoxysilane (KH560) and γ-methacryloxypropyltrimethoxysilane (KH570)] and used as a decolourizer for bleaching of refined palm oil. The effects of different silane coupling agents on the structure, surface charges and pore structure of ATP were investigated by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, Zeta potential and nitrogen adsorption-desorption isotherm techniques, and the decolourization efficiency of the modified ATP was evaluated by UV-Vis absorbance and Lovibond colour. The results show that the KH550-modified ATP exhibits the best decolourization performance, which can decrease the red-yellow value of refined palm oil by 31.96% and the phosphorus content by 77.69% after bleaching; while the unmodified ATP can only decrease these values by 17.30% and 62.31%, respectively.

In situ generation of silver nanoparticles within crosslinked 3D guar gum networks for catalytic reduction

The direct use of guar gum (GG) as a green reducing agent for the facile production of highly stable silver nanoparticles (Ag NPs) within this biopolymer and subsequent crosslinking with borax to form crosslinked Ag@GG beads with a 3D-structured network are presented here. These crosslinked Ag@GG beads were characterized using UV-vis absorption spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy, and then tested as a solid-phase heterogenerous catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of excess borohydride. The results indicate that these crosslinked Ag@GG beads show excellent catalytic performance for the reduction of 4-NP within 20 min and can be readily used for 10 successive cycles.

All-into-one strategy to synthesize mesoporous hybrid silicate microspheres from naturally rich red palygorskite clay as high-efficient adsorbents

A mesoporous hybrid silicate microsphere with superior adsorption performance has been successfully synthesized by employing an “all-into-one” strategy and a simple one-pot hydrothermal process using naturally abundant low-grade red palygorskite (PAL) clay as raw material in the presence of non-toxic SiO32− and Mg2+ ions. As is expected, both the PAL and associated minerals transformed into a new amorphous mesoporous hybrid silicate microsphere without using any additional pore-forming template. The mesoporous silicate microsphere shows a large pore size of 37.74 nm, high specific surface area of 489.81 m2/g (only 54.67 m2/g for raw PAL) and negative surface potential of −43.3 mV, and its maximum adsorption capabilities for Methylene bule (MB) and Crystal violet (CV) reach 407.95 mg/g and 397.22 mg/g, respectively. Meanwhile, 99.8% of MB (only 53% for raw PAL) and 99.7% of CV (only 43% for raw PAL) were sucessfully removed from 200 mg/L of initial dye solution by only using 1 g/L of the adsorbent. In addition, the spent adsorbent can be easily regenerated and repeatly reused for muptiple cycles. The study on adsorption mechanism revealed that electrostatic attraction, hydrogen bonding and chemical complexing interactions are the main factors contributed to the high dye adsorption.

Ag(I)-triggered one-pot synthesis of Ag nanoparticles onto natural nanorods as a multifunctional nanocomposite for efficient catalysis and adsorption.

A multifunctional palygorskite/polyaniline/Ag nanoparticles (PAL/PANI/AgNPs) nanocomposite was prepared at room temperature using a simple one-pot in-situ polymerization reaction of aniline monomers triggered by Ag(I) on the surface of natural PAL nanorods. Ag(I) served as both the oxidant and the precursor of the AgNPs, which initiated the polymerization of aniline monomers on PAL nanorods while simultaneously being reduced to form Ag(0) nanoparticles (AgNPs). The in-situ formed AgNPs were evenly distributed on the surface of the PAL nanorods because the interfacial effect of PAL prevents their aggregation. The density and size of the AgNPs and the catalytic activity of the nanocomposites could be controlled by altering the molar ratio of aniline to Ag(I). The performance evaluation revealed that the nanocomposites could be used as highly active catalysts, which rapidly catalyzed the reduction of 4-nitrophenol (4-NP) within 2min and Congo red (CR) within 10min. The nanocomposites are also an effective adsorbent for H2PO4(-) able to remove 99.40% of H2PO4(-) (only 61.77% for raw PAL) from a solution with an initial concentration of 50mg/L. This multifunctional nanocomposite synthesized by a simple one-pot approach is a promising material for environmental applications.

From spent dye-loaded palygorskite to a multifunctional palygorskite/carbon/Ag nanocomposite

Palygorskite (PAL) has been widely used for adsorption removal of dyes from wastewater, but the dye-loaded PAL is usually discharged as solid waste because it is hardly regeneratable by conventional elution processes. As the aim was to efficiently utilize the dye-loaded PAL waste, we employed a facile one-pot hydrothermal process to transform the spent methyl violet (MV)-loaded PAL into multifunctional ternary palygorskite/carbon/Ag nanoparticles (PAL/C/AgNPs) nanocomposites in the assistance of AgNO3. The MV-loaded PAL serves as a carbon precursor, reducer of Ag(I) and supporter of the in situ formed AgNPs. Structure characterizations confirmed that the MV dye was transformed into carbon species, and AgNPs were formed on the PAL with good dispersion, and the addition of Ag(I) ions promoted carbonization of the MV molecules. The as-prepared nanocomposites exhibited excellent adsorption and catalytic performance. Adsorption evaluation showed that the nanocomposite prepared at 5 mass% of AgNO3 dosage gives the best adsorption properties, and 99.2% of methylene blue (MB), 86.9% of MV, 68.7% of chlortetracycline hydrochloride (CTC) and 46.2% of tetracyclines (TC) were rapidly removed from 100 mg L−1 of the aqueous solution using 0.5 g L−1 of the adsorbent. The removal ratio increased with increasing dosage of adsorbent, and the minimum usage amounts of adsorbent for the thorough removal of MB, MV, CTC and TC molecules were 1.0 g L−1, 1.2 g L−1, 3.5 g L−1 and 4.5 g L−1, respectively. Moreover, the nanocomposites could rapidly catalyze the conversion of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) within 6.5 min with a catalytic rate constant of 0.0120 s−1, and the catalytic activity is still retained after 8 cycles of reuse. In addition, the nanocomposite can be re-generated into new adsorbents by the same hydrothermal process after adsorption of organic matters, which open a new sustainable avenue to efficiently utilize waste dye-loaded PAL and develop new adsorption and catalysis materials.

Carbon/Attapulgite Composites as Recycled Palm Oil-Decoloring and Dye Adsorbents

Activated clay minerals have been widely used in the edible oil refining industry for decolorization of crude oil by adsorption, and so far many methods have been used to improve their decolorization efficiency. Herein, we successfully prepared a series of carbon/attapulgite (C/APT) composite adsorbents by a one-step in-situ carbonization process with natural starch (St) as the carbon source. It has been revealed that the adsorbent had better decolorization efficiency for crude palm oil than acid-activated APT. However, more than a million tons of decolorized waste is produced every year in the oil-refining industry, which was often treated as solid waste and has not yet been reutilized effectively. In order to explore a viable method to recycle and reuse the decolorant, the waste decolorant was further prepared into new C/APT adsorbents for the removal of dyes from wastewater, and then the dyes adsorbed on the adsorbent were used as the carbon sources to produce new C/APT adsorbents by a cyclic carbonization process. The results showed that the adsorbents prepared from the decolorized waste could remove more than 99.5% of the methylene blue (MB), methyl violet (MV), and malachite green (MG) dyes from the simulated wastewater with the dye concentration of 200 mg/L, and the C/APT–Re adsorbent consecutively regenerated five times using the adsorbed dyes as a carbon source still exhibit good adsorption efficiency for dyes. As a whole, this process opens a new avenue to develop efficient decolorants of palm oil and achieves recyclable utilization of decolored waste.