[en] Uniform and sphere-like nanoparticles of crystalline Pr³⁺-doped CaTiO₃ have been prepared from complex polymer precursor at 600 deg. C, in which, metal atoms are previously dispersed by citric acid in ethylene glycol solvent. The decomposition process of the precursor, crystallization, and particle sizes of CaTiO₃ have been investigated by using thermal analysis, powder X-ray diffraction and transmission electron microscopy. Diffuse reflectance spectra, photoluminescence and decay curve indicate that a strong red emission located at the nearly NTCS 'ideal red' site is deduced from the energy transfer from the band gap absorption to doping Pr³⁺ ions. The thermoluminescence curves exhibit that a potential long phosphorescent material based on Pr³⁺-doped CaTiO₃ will be explored in future

[en] Phosphorus-rich sludge is one of most suitable raw materials for phosphorus recovery as slow release fertilizers by struvite crystallization. However, alginic acid as a surrogate for extracellular polymeric substances in the sludge has been proved to adversely inhibit struvite crystallization. To quantitatively evaluate the inhibitory effect, the study aimed to investigate the influence of the concentration of alginic acid (0–250 mg/L), reactant concentration (2.5–3.5 mmol/L), pH (8.0–9.5), and ionic strength (0.01–0.2 mol/L NaCl), on the inhibition of the growth rate of struvite crystals, which was accurately determined by constant composition technique. The results indicated that the growth rate of struvite crystals substantially decreased with increasing the concentration of alginic acid, thereby adversely affecting the quantity and quality of struvite crystals. Moreover, as reactant concentration or pH increased, the growth rate of struvite crystals showed a considerable increase, whereas the weaker inhibitory effect of alginic acid was observed. Conversely, the increase of ionic strength drastically reduced the growth rate of struvite crystals, but moderately enhanced the inhibitory effect. Our study provides an effective theoretical foundation for deriving high-quality struvite crystals as slow release fertilizers from the phosphorus-rich sludge commonly containing a considerable number of organic pollutants.

[en] In this study, Mn-substituted siderites with different substitution amounts were prepared and characterized by using XRD (X-ray diffraction), TEM (transmission electron microscope), TG and DTG (thermogravimetry and derivative thermogravimetry) and Raman spectroscopy. The effect of Mn substitution on the crystal structure of siderite and thermal decomposition processes of synthetic siderite was investigated. The substitution of Mn for Fe in the crystal structure of siderite resulted in an increase in a and c dimensions from 4.702 and 15.374 to 4.718 and 15.43 Å as the substitution amount increased from 0 to 7.4%, respectively. The substitution of Mn also decreased the crystallinity of siderite. The thermal decomposition of synthetic siderite took place at approximately 350 °C. However, the substitution of Mn for Fe increased the decomposition temperature and improved the activation energy (E_d) values from 126.3, 155.7, 156.8 to 164.5, 167.6, 170.3 kJ mol⁻¹ when Mn substitution increased from 0 to 7.4 mol%.

[en] Highlights: • Siderite is effective to activate PDS to degrade sulfadiazine. • The role of singlet oxygen under different pH value is investigated. • The staged kinetic fitting describes the role of ROS. • The unique intermediate caused by ¹O₂ is illustrated. Occurring naturally siderite (FeCO₃) was used as the heterogeneous catalyst to activate peroxodisulfate (PDS) for the degradation of sulfadiazine under different initial pH values. The findings of this system exhibited various ROS (e.g. ¹O₂, SO₄⁻ and OH) present during a wide range of pH values. Among them, ¹O₂ could significantly facilitate the initial degradation rate, and the increased pH enhanced the role of ¹O₂. The factors including initial pH values, siderite dosage, PDS concentration, initial contaminants concentration, and water matrix were discussed. The role of each ROS was investigated through quenching test and electron paramagnetic resonance (EPR). Furthermore, the comprehensive degradation process was proposed based on the LC-MS results. And the cycle test demonstrates the reusability of siderite at a pH of 3. Accordingly, this study is of great significance for understanding the degradation of such sulfonamide pollutants in the siderite/PDS system.

[en] The removal behavior and characteristic of cadmium (Cd²⁺) on wheat straw char activated by CO₂ were investigated in this study. The equilibrium, kinetics, and removal isotherms were studied. The results of batch experiments revealed that the removal of Cd²⁺ was described well by pseudo-second-order and Langmuir models. The increase in activation time improved the removal of Cd²⁺, especially for the activation time of 84 min. The results suggested that chemisorption of Cd²⁺ on activated carbon was the main reaction mechanism. The maximum removal capacity of Cd²⁺ onto activated WSC-84 was 75.55 mg/g, which was much higher than other three samples activated by CO₂ with other amounts of time. According to the results of SEM, XPS, and FT-IR, complexation with surface oxygen-containing functional groups, ion exchange, and precipitation were the possible mechanisms of the removal process. It is suggested that the experimental results will enhance the comprehensive understanding of the activation of biomass and its utilization in the restoration of Cd-contaminated soil.

[en] Nano zero valent iron (NZVI) was prepared by reducing natural limonite using hydrogen. X-ray fluorescence, thermogravimetry, X-ray diffraction, transmission electron microscope, temperature programmed reduction (TPR), field emission scanning electron microscope/energy disperse spectroscopy (FESEM/EDS) were utilized to characterize the natural limonite and reduced limonite. The ratios of Fe:O before and after reducing was determined using EDS. The reactivity of the NZVI was assessed by decomposition of p-nitrophenol (p-NP) and was compared with commercial iron powder. In this study, the results of TPR and FESEM/EDS indicated that NZVI can be prepared by reducing natural limonite using hydrogen. Most importantly, this NZVI was proved to have a good performance on decomposition of p-NP and the process of p-NP decomposition agreed well with the pseudo-first-order kinetic model. The reactivity of this NZVI for decomposition of p-NP was greatly superior to that of commercial iron powder

[en] Highlights: • U(VI) was primarily adsorbed on pyrrhotite and partially reduced by Fe"2"+ and S"2"−. • XAS demonstrated reductive co-precipitates of U(VI) on pyrrhotite after 168 h. • Inner-surface complexation dominated the U(VI) removal at pH > 5 by SCMs. - Abstract: The interaction mechanism of U(VI) on pyrrhotite was demonstrated by batch, spectroscopic and modeling techniques. Pyrite was selected as control group in this study. The removal of U(VI) on pyrite and pyrrhotite significantly decreased with increasing ionic strength from 0.001 to 0.1 mol/L at pH 2.0–6.0, whereas the no effect of ionic strength was observed at pH  > 6.0. The maximum removal capacity of U(VI) on pyrite and pyrrhotite calculated from Langmuir model was 10.20 and 21.34 mg g"−"1 at pH 4.0 and 333 K, respectively. The XPS analysis indicated the U(VI) was primarily adsorbed on pyrrhotite and pyrite and then approximately 15.5 and 9.8% of U(VI) were reduced to U(IV) by pyrrhotite and pyrite after 20 days, respectively. Based on the XANES analysis, the adsorption edge of uranium-containing pyrrhotite located between U"I"VO_2(s) and U"V"IO_2"2"+ spectra. The EXAFS analysis demonstrated the inner-sphere surface complexation of U(VI) on pyrrhotite due to the occurrence of U-S shell, whereas the U-U shell revealed the reductive co-precipitates of U(VI) on pyrrhotite/pyrite with increasing reaction times. The surface complexation modeling showed that outer- and inner-surface complexation dominated the U(VI) removal at pH < 4 and pH > 5.0, respectively. The findings presented herein play a crucial role in the removal of radionuclides on iron sulfide in environmental cleanup applications.

[en] Highlights: • Siderite effectively activate H₂O₂ to produce ·OH over a wide pH values range. • Siderite has a high potential to remove micropollutants (MPs) in subsurface with H₂O₂. • The detailed kinetic fitting describes the influence of parameters. • The role of lattice Fe(Ⅱ) in activating H₂O₂ is demonstrated. Siderite is a conventional mineral of sedimentary rock and can activate H₂O₂ to produce hydroxyl radicals (·OH). Bisphenol A (BPA), 2,4-dichlorophenoxyacetic acid (2,4-D), and sodium sulfadiazine are selected as typical micropollutants to be degraded in a siderite-activated H₂O₂ system. To determine the influence of solution chemistry on siderite-activated Fenton-like reactions, the amount of ·OH was quantified by using benzoic acid as a probe molecule, and then, kinetic fitting was used to analyze the reaction rate. The results showed that in the range of pH values from 3 to 9, the dissolved Fe²⁺ and the lattice Fe(Ⅱ) of siderite activate H₂O₂ to generate ·OH. An increase in siderite dosage and H₂O₂ concentration favored the generation of ·OH, but higher siderite dosage and H₂O₂ concentration suppressed the production rate. The inhibition order of anions on the generation of ·OH was confirmed as follows $C{l}^{-}$ > $N{O}_3^{-}$ > $S{O}_4^{2-}$. Little difference was observed in the presence of Ca²⁺ and Mg²⁺, while the presence of Mn²⁺ significantly promoted the production of ·OH. The suppression of humic acid (HA) became more serious as the HA concentration increased. Cycling experiments proved that the system could still produce ·OH in four cycles, although the production rate experienced a slight decrease. The experimental results suggested the role of siderite in the degradation of organic pollution in the process of in-situ soil and groundwater remediation.

[en] This study investigated a wastewater treatment technique based on natural minerals. A two-step process using manganese (Mn) and magnesium (Mg) containing ores were tested to remove typical contaminants from coking wastewater. Under acidic conditions, a reactor packed with Mn ore demonstrated strong oxidizing capability and destroyed volatile phenols, chemical oxygen demand (COD)_, and sulfide from the coking wastewater. The effluent was further treated by using Mg ore to remove ammonium-nitrogen and phosphate in the form of magnesium ammonium phosphate (struvite) precipitates. When pH of the wastewater was adjusted to 1.2, the removal efficiencies for COD, volatile phenol and sulfide reached 70%, 99% and 100%, respectively. During the second step of precipitation, up to 94% of ammonium was removed from the aqueous phase, and precipitated in the form of struvite with phosphorus. The struvite crystals showed a needle-like structure. X-ray diffraction and transmission electron microscopy were used to characterize the crystallized products.

[en] Graphical abstract: - Highlights: • Co₃O₄/β-PbO₂ electrode was prepared and an excellent electrocatalytic property. • Co₃O₄/β-PbO₂ electrode had good corrosion resistance characterization and lifetime. • BPA electrocatalytic degradation followed pseudo-first-order reaction process. - Abstract: Ti-base Co₃O₄/β-PbO₂ composite electrodes were prepared using electro-deposition and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry and the accelerated life testing, it indicated that the self-made electrode had high activity in electrolysis as well as excellent corrosion resistance and excellent catalytic performance. The results showed that the removal efficiency of COD_Cr could be reached up to 92.2% after 1.5 h electrolysis at NaCl concentration of 0.020 mol·L⁻¹, bisphenol A initial concentration of 20 mg·L⁻¹, applied voltage of 20 V, electrode spacing of 7 cm and electrolyte pH of 5. The reaction mechanism and kinetics of Co₃O₄/β-PbO₂/Ti composite electrodes electro-catalytic degradation bisphenol A mainly caused by the OH radical attacking parent molecules and the degradation followed pseudo-first-order kinetics