Long-term unregulated mining of ion-adsorption clays (IAC) in China has resulted in severe ecological destruction and created large areas of wasteland in dire need of rehabilitation. Soil amendment and revegetation are two important means of rehabilitation of IAC mining wasteland. In this study, we used sludge biochar prepared by pyrolysis of municipal sewage sludge as a soil ameliorant, selected alfalfa as a revegetation plant, and conducted pot trials in a climate-controlled chamber. We investigated the effects of alfalfa revegetation, sludge biochar amendment, and their combined amendment on soil physicochemical properties in soil from an IAC mining wasteland as well as the impact of sludge biochar on plant growth. At the same time, we also assessed the impacts of these amendments on the soil microbial community by means of the Illumina Miseq sequences method. Results showed that alfalfa revegetation and sludge biochar both improved soil physicochemical properties and microbial community structure. When alfalfa revegetation and sludge biochar amendment were combined, we detected additive effects on the improvement of soil physicochemical properties as well as increases in the richness and diversity of bacterial and fungal communities. Redundancy analyses suggested that alfalfa revegetation and sludge biochar amendment significantly affected soil microbial community structure. Critical environmental factors consisted of soil available K, pH, organic matter, carbon–nitrogen ratio, bulk density, and total porosity. Sludge biochar amendment significantly promoted the growth of alfalfa and changed its root morphology. Combining alfalfa the revegetation with sludge biochar amendment may serve to not only achieve the revegetation of IAC mining wasteland, but also address the challenge of municipal sludge disposal by making the waste profitable.

Rare earth element La-doped TiO2 (La/TiO2) was synthesized by the sol-gel method. Benzohydroxamic acid was used as the objective pollutant to investigate the photocatalytic activity of La/TiO2. The physicochemical properties of the prepared materials were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, specific surface area and porosity, scanning electron microscopy and transmission electron microscopy. As a result, the doping of La could inhibit the crystal growth of TiO2, increase its specific surface area and expand its response to visible light, thus improving its photocatalytic activity. La/TiO2 with the doping ratio of 0.75% calcined at 500 °C, showing the highest photocatalytic activity to degrade benzohydroxamic acid under the irradiation of 300 W mercury lamp. About 94.1% of benzohydroxamic acid with the original concentration at 30 mg·L−1 was removed after 120 min in a solution of pH 4.4 with an La/TiO2 amount of 0.5 g·L−1. Furthermore, 88.5% of the total organic carbon was eliminated after 120 min irradiation. In addition, after four recycling runs, La/TiO2 still kept high photocatalytic activity on the photodegradation of benzohydroxamic acid. The interfacial charge transfer processes were also hypothesized.

Photolysis and photocatalysis of typical phthalic acid esters (dimethyl phthalate, DMP; diethyl phthalate, DEP; dibutyl phthalate, DBP) were carried out in UV, UV/TiO 2 , and UV-Vis/Bi 2 WO 6 systems. All of the selected phthalic acid esters and their decomposition byproducts were subjected to qualitative and quantitative analysis through HPLC and GC-MS. The results of 300 min of photolysis and photodegradation reaction were that each system demonstrated different abilities to remove DMP, DEP, and DBP. The UV/TiO 2 system showed the strongest degradation ability on selected PAEs, with removal efficiencies of up to 93.03, 92.64, and 92.50% for DMP, DEP, and DBP in 90 min, respectively. UV-Vis/Bi 2 WO 6 had almost no ability to remove DMP and DEP. However, all of the systems had strong ability to degrade DBP. On the other hand, the different systems resulted in various byproducts and PAE degradation pathways. The UV system mainly attacked the carbon branch and produced o-hydroxybenzoates. No ring-opening byproducts were detected in the UV system. In the photocatalytic process, the hydroxyl radicals produced not only attacked the carbon branch but also the benzene ring. Therefore, hydroxylated compounds and ring-opening byproducts were detected by GC-MS in both the UV/TiO 2 and UV-Vis/Bi 2 WO 6 photocatalytic systems. However, there were fewer products due to direct hole oxidation in the UV-Vis/Bi 2 WO 6 system compared with the UV/TiO 2 system, which mainly reacted with the pollutants via hydroxyl radicals.

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Yb-doped TiO2 (Yb/TiO2) compositions were synthesized by sol-gel method, and the prepared materials were characterized by X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse-reflectance spectrum (UV-Vis DRS), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM), energy dispersive spectrometer (EDS), and N2 adsorption. A beneficiation reagent of benzohydroxamic acid (BHA) was used to test the photocatalytic activity of Yb/TiO2. The characterizations indicate that the doping of Yb could inhibit the crystal growth of TiO2, enhance the specific surface area, increase the binding energy of Ti2p, and also slightly expand the adsorption ranges to visible light. Furthermore, the computation of band structure also indicates that Yb-doped TiO2 could make the forbidden band narrower than pure anatase TiO2, which presents a red shift in the absorption spectrum. As a result of the photodegradation experiment on BHA, Yb/TiO2 (0.50% in mass) sintered at 450 °C displayed the highest catalytic activity for BHA when compared with pure TiO2 or other doped Yb/TiO2 compositions, and more than 89.2% of the total organic carbon was removed after 120 min. Almost all anions, including Cl−, HCO3−, NO3−, and SO42−, inhibited the degradation of BHA by Yb/TiO2, and their inhibition effects followed the order of HCO3− > NO3− > SO42− > Cl−. Cations of Na+, K+, Ca2+, and Mg2+ displayed a slight suppressing effect due to the impact of Cl− coexisting in the solution. In addition, Yb/TiO2 maintained a high photocatalytic ability with respect to BHA after four runs. It is hypothesized that ·OH is one of the main species involved in the photodegradation of BHA, and the mutual transformation of Yb3+ and Yb2+ could promote the separation of electron-hole pairs.