In Situ Confined Synthesis of a Copper-Encapsulated Silicalite-1 Zeolite for Highly Efficient Iodine Capture.

Effective capture of radioactive iodine is highly desirable for decontamination purposes in spent fuel reprocessing. Cu-based adsorbents with a low cost and high chemical affinity for I2 molecules act as a decent candidate for iodine elimination, but the low utilization and stability remain a significant challenge. Herein, a facile in situ confined synthesis strategy is developed to design and synthesize a copper-encapsulated flaky silicalite-1 (Cu@FSL-1) zeolite with a thickness of ≤300 nm. The maximum iodine uptake capacity of Cu@FSL-1 can reach 625 mg g-1 within 45 min, which is 2 times higher than that of a commercial silver-exchanged zeolite even after nitric acid and NOX treatment. The Cu nanoparticles (NPs) confined within the zeolite exert superior iodine adsorption and immobilization properties as well as high stability and fast adsorption kinetics endowed by the all-silica zeolite matrix. This study provides new insight into the design and controlled synthesis of zeolite-confined metal adsorbents for efficient iodine capture from gaseous radioactive streams.

Highly-efficient and easy separation of γ-Fe2O3 selectively adsorbs U(⠥) in waters.

The migration and transformation of uranyl [U (Ⅵ)] ions in the environment are quite dependent on the geological condition in particular with the site enriched in Fe. In this study, the interfacial interaction of U (Ⅵ) ions with maghemite (γ-Fe2O3) particles was studied and the interaction mechanism was explored as well. Batch experiments confirm that γ-Fe2O3 can effectively remove U (Ⅵ) from an aqueous solution within a relatively short reaction time (R% > 92.01% within 3 min) and has a considerable capacity for U (Ⅵ) uptake (qt: 87.35 mg/g). γ-Fe2O3 displays an excellent selectivity for U (Ⅵ) elimination. Results on the effects of natural organic matter such as humic acid (HA) indicated that HA could promote the interfacial interaction between γ-Fe2O3 and U (Ⅵ) under acidic conditions. Compared with other radionuclides (e.g., Sr(Ⅱ) and Cs(Ⅰ)), U (Ⅵ) was more effectively removed by γ-Fe2O3. The U (Ⅵ) removal by γ-Fe2O3 is primarily due to electrostatic interactions and precipitation that result in the long-term retardation of uranium. γ-Fe2O3 not only can fast and selectively adsorb U (Ⅵ) but also can be magnetically recycled, demonstrating that γ-Fe2O3 is a cost-effective and promising material for the clean-up of uranyl ions from radioactive wastewater.

Pb Stabilization by a New Chemically Durable Orthophosphate Phase: Insights into the Molecular Mechanism with X-ray Structural Analysis.

The rapid progression of piezoelectric technology and the upgradation of electronic devices have resulted in a global increase in Pb-based piezoelectric ceramic materials. In this study, the feasibility of incorporating Pb into a PbZr(PO4)2 double orthophosphate structure was evaluated by investigating the interaction mechanism of the perovskite with phosphate. The unique combination of X-ray absorption spectroscopy, selected area electronic diffraction, and Pawley refinement revealed that Pb was incorporated into a hexagonal structure and tetra-coordinated with oxygen in the phosphate-treated product. The chemical durability was enhanced through the structural alterations via Zr-O-P and Pb-O-P bond linkages. The stable phase encapsulating both Pb and phosphate showed effectiveness not only in stabilizing Pb but also in inhibiting P release as a secondary pollution risk within a wide pH range (1 ≤ pH ≤ 13). Despite the excellent chemical durability of the robust PbZr(PO4)2 crystalline phase, the increased Ti doping amounts at the Zr site resulted in a slight decrease in the lattice parameters and further enhanced the Pb stabilization effect through the formation of PbZrxTi(1-x)(PO4)2 solid solutions. This study demonstrates that the newly robust crystalline structure, developed through a well-designed thermal treatment scheme, provides an effective strategy for the treatment of Pb frequently encountered in electronic wastes.

Unraveling the Structure of the Poly(triazine imide)/LiCl Photocatalyst: Cooperation of Facile Syntheses and a Low-Temperature Synchrotron Approach.

Graphitic carbon nitride (g-C3N4)-based materials have attracted interdisciplinary attention from many fields. However, their crystal structures have not yet been described well. Poly(triazine imide)/LiCl (PTI/LiCl) of good crystallinity synthesized from salt melts enables a confident structural solution for a better understanding of g-C3N4-based materials. In this study, we synthesize PTI/LiCl of high crystallinity in air without byproducts and confirm the orthorhombic feature, which is not observed in powder X-ray diffraction (PXRD) patterns at room temperature, by employing low-temperature synchrotron PXRD. Together with spectroscopic techniques (X-ray photoelectron spectroscopy, solid-state nuclear magnetic resonance, and Fourier-transform infrared/Raman), the orthorhombic structure (space group Cmc21, No. 36) was determined and found to be a superstructure of the previously reported hexagonal structure, as confirmed by electron diffraction. The temperature-dependent synchrotron PXRD data also reveal a highly anisotropic expansion. This work also shows the much higher activity of PTI/LiCl than of g-C3N4 for the photocatalytic degradation of methyl orange under ultraviolet irradiation, especially so for PTI/LiCl with a densely packed (001) plane. This study demonstrates the structural complexity of the g-C3N4 class of materials and illustrates how their temperature-dependent anisotropies facilitate the discovery of the structural features in resolving the structure of g-C3N4-related materials and their structure-property relationship.

Incorporation of Cadmium and Nickel into Ferrite Spinel Solid Solution: X-ray Diffraction and X-ray Absorption Fine Structure Analyses.

The feasibility of incorporating Cd and Ni in hematite was studied by investigating the interaction mechanism for the formation of CdxNi1-xFe2O4 solid solutions (CNFs) from CdO, NiO, and α-Fe2O3. X-ray diffraction results showed that the CNFs crystallized into spinel structures with increasing lattice parameters as the Cd content in the precursors was increased. Cd2+ ions were found to occupy the tetrahedral sites, as evidenced by Rietveld refinement and extended X-ray absorption fine structure analyses. The incorporation of Cd and Ni into ferrite spinel solid solution strongly relied on the processing parameters. The incorporation of Cd and Ni into the CNFs was greater at high x values (0.7 < x ≤ 1.0) than at low x values (0.0 ≤ x ≤ 0.7). A feasible treatment technique based on the investigated mechanism of CNF formation was developed, involving thermal treatment of waste sludge containing Cd and Ni. Both of these metals in the waste sludge were successfully incorporated into a ferrite spinel solid solution, and the concentrations of leached Cd and Ni from this solid solution were substantially reduced, stabilizing at low levels. This research offers a highly promising approach for treating the Cd and Ni content frequently encountered in electronic waste and its treatment residues.

Quantification of the Partitioning Ratio of Minor Actinide Surrogates between Zirconolite and Glass in Glass-Ceramic for Nuclear Waste Disposal.

Zirconolite-based glass-ceramic is considered a promising wasteform for conditioning minor actinide-rich nuclear wastes. Recent studies on this wasteform have sought to enhance the partitioning ratio (PR) of minor actinides in zirconolite crystal. To optimize the PR in the SiO2-Al2O3-CaO-TiO2-ZrO2 system, a novel conceptual approach, which can be derived from the chemical composition and quantity of zirconolite crystal in glass-ceramic, was introduced based on the results of Rietveld quantitative X-ray diffraction analysis and transmission electron microscopy energy dispersive X-ray spectroscopy. To verify this new conceptual approach, the influences of the crystallization temperature, the concentration of additives, and ionic radii on the PR of various surrogates (Ce, Nd, Gd, and Yb) in zirconolite were examined. The results reveal that the PR of Nd3+ in zirconolite can be as high as 41%, but it decreases as the crystallization temperature increases. The quantities of all phases (including crystalline and amorphous) remained nearly constant when increasing the loading of Nd2O3 in glass-ceramic products crystallized at 1050 °C for 2 h. Correspondingly, the PR of Nd3+ decreases in a linear fashion with the loading contents of Nd2O3. The radius of ions also has a great influence on the PR, and an increase in the ionic radius leads to a decrease in the PR. This new approach will be an important tool to facilitate the exploration of a glass-ceramic matrix for the disposal of minor actinide-rich nuclear wastes.

Changes in the microbial community during repeated anaerobic microbial dechlorination of pentachlorophenol.

Pentachlorophenol (PCP) has been widely used as a pesticide in paddy fields and has imposed negative ecological effect on agricultural soil systems, which are in typically anaerobic conditions. In this study, we investigated the effect of repeated additions of PCP to paddy soil on the microbial communities under anoxic conditions. Acetate was added as the carbon source to induce and accelerate cycles of the PCP degradation. A maximum degradation rate occurred at the 11th cycle, which completely transformed 32.3 µM (8.6 mg L-1) PCP in 5 days. Illumina high throughput sequencing of 16S rRNA gene was used to profile the diversity and abundance of microbial communities at each interval and the results showed that the phyla of Bacteroidates, Firmicutes, Proteobacteria, and Euryarchaeota had a dominant presence in the PCP-dechlorinating cultures. Methanosarcina, Syntrophobotulus, Anaeromusa, Zoogloea, Treponema, W22 (family of Cloacamonaceae), and unclassified Cloacamonales were found to be the dominant genera during PCP dechlorination with acetate. The microbial community structure became relatively stable as cycles increased. Treponema, W22, and unclassified Cloacamonales were firstly observed to be associated with PCP dechlorination in the present study. Methanosarcina that have been isolated or identified in PCP dechlorination cultures previously was apparently enriched in the PCP dechlorination cultures. Additionally, the iron-cycling bacteria Syntrophobotulus, Anaeromusa, and Zoogloea were enriched in the PCP dechlorination cultures indicated they were likely to play an important role in PCP dechlorination. These findings increase our understanding for the microbial and geochemical interactions inherent in the transformation of organic contaminants from iron rich soil, and further extend our knowledge of the PCP-transforming microbial communities in anaerobic soil conditions.

Crystal Structures of Al-Nd Codoped Zirconolite Derived from Glass Matrix and Powder Sintering.

Zirconolite is a candidate host for immobilizing long-lived radionuclides. Zirconolite-based glass-ceramics in the CaO-SiO2-Al2O3-TiO2-ZrO2-Nd2O3-Na2O matrix are a potential waste form for immobilizing actinide radionuclides and can offer double barriers to immobilize radioactive elements. However, the X-ray diffraction patterns of the zirconolite derived from the glass matrix (glass ceramic, GC) are significantly different from those prepared by powder sintering (PS). In this Article, the crystal structures of Al-Nd codoped zirconolite grown via the glass matrix route and the powder sintering route are investigated in detail. Two samples of Al-Nd codoped zirconolite were prepared: one was grown from a CaO-SiO2-Al2O3-TiO2-ZrO2-Nd2O3-Na2O glass matrix, and the other was prepared with a Ca0.75Nd0.25ZrTi1.75Al0.25O7 composition by powder sintering. The samples were then characterized using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX), and selected area electron diffraction (SAED). The chemical composition of the 100-500 nm zirconolite crystals grown from a glass matrix was determined by TEM-EDX to be Ca0.83Nd0.25Zr0.85Ti1.95Al0.11O7. PXRD and SAED results showed that these two Al-Nd codoped zirconolite phases were crystallized in space group C12/c1. The HRTEM images and SAED results showed that there were heavy stacking faults in the zirconolite crystals grown from the glass matrix. In contrast, far fewer defects were found in the zirconolite crystals prepared by powder sintering. The split-atom model was adopted for the first time to construct the Al-Nd codoped zirconolite structure grown from glass during the Rietveld refinement. The isostructural method assisted by Rietveld refinement was used to resolve the Al-Nd codoped zirconolite structures prepared by different methods. The occupancies of the cation sites were identified, and the distribution behavior of Nd(3+) was further investigated. The results indicate that the heavy stacking faults may lead to substantial differences in the Al-Nd codoped zirconolite structures prepared by these two fabrication routes.

In situ synthesis of TiO2(B) nanotube/nanoparticle composite anode materials for lithium ion batteries.

Titania nanotubes were prepared by a simple hydrothermal route. Their electrochemical performance has been examined in detail and compared to TiO2(B) nanoparticles, TiO2 anatase and P25 titania nanoparticles. The cycling and rate performance of TiO2 nanotubes is superior to both types of nanoparticles, and it can be further improved by an in situ titanium precursor treatment, which results in the formation of TiO2 nanoparticles on/between the nanotubes. The obtained specific capacity after 200 cycles at 0.2 A g(-1) charge/discharge rate remained above 130 mAh g(-1). The enhanced lithium storage properties of these samples can be attributed to their unique morphology and crystal structure.

Cadmium Stabilization Efficiency and Leachability by CdAl4O7 Monoclinic Structure.

This study investigated the stabilization efficiencies of using an aluminum-rich precursor to incorporate simulated cadmium-bearing waste sludge and evaluated the leaching performance of the product phase. Cadmium oxide and γ-alumina mixtures with various Cd/Al molar ratios were fired at 800-1000 °C for 3 h. Cadmium could be crystallochemically incorporated by γ-alumina into CdAl4O7 monoclinic phase and the reaction was strongly controlled by the treatment temperature. The crystal structure details of CdAl4O7 were solved and refined with the Rietveld refinement method. According to the structural refinement results, the stabilization efficiencies were quantified and expressed as a transformation ratio (TR) with optimized processing parameters. The preferred treatment temperature was found to be 950 °C for mixtures with a Cd/Al molar ratio of 1/4, as its TR value indicated the cadmium incorporation was nearly completed after a 3 h treatment scheme. Constant-pH leaching tests (CPLT) were conducted by comparing the leachability of the CdO and CdAl4O7 phases in a pH 4.0 environment. A remarkable reduction in cadmium leachability could be achieved via monoclinic CdAl4O7 structure formation to effectively stabilize hazardous cadmium in the waste stream. The CPLT and X-ray photoelectron spectroscopy (XPS) results suggested incongruent dissolution behavior during the leaching of the CdAl4O7 phase.

Green conversion of waste alkaline battery material to zeolitic imidazolate framework-8 and its iodine capture mechanism.

Zeolitic imidazolate framework-8 (ZIF-8) exhibits excellent performance in capturing iodine. However, the solvent-based procedures and raw materials for ZIF-8 synthesis often lead to secondary pollution. We developed a solvent-minimizing method for preparing ZIF-8 via ball milling of raw material obtained from spent alkaline batteries, and studied its iodine-capture performance and structural changes. Exposure of the ZIF-8 to iodine vapor for 60 min demonstrated that it exhibited industrially competitive iodine-capture performance (the adsorbed amount reaches to 1123 mg g-1 within 60 min). Spectroscopic studies showed that ZIF-8 underwent a structural transformation upon iodine loading. Iodine molecules were adsorbed onto the surface of ZIF-8 and also formed C-I bond with the methyl groups on the imidazole rings, reducing iodine release. This work represents a comprehensive revelation of long-range order and short-range order evolution of ZIF-8 during iodine vapor adsorption over time. Moreover, this green synthesis of ZIF-8 is of lower cost and generates fewer harmful by-products than existing methods, and the produced ZIF-8 effectively entraps toxic iodine vapor. Thus, this synthesis enables a sustainable and circular material flow for beneficial utilization of waste materials.

Recent advances toward structural incorporation for stabilizing heavy metal contaminants: A critical review.

Heavy metal pollution has resulted in serious environmental damage and raised significant public health concerns. One potential solution in terminal waste treatment is to structurally incorporate and immobilize heavy metals in some robust frameworks. Yet extant research offers a limited perspective on how metal incorporation behavior and stabilization mechanisms can effectively manage heavy metal-laden waste. This review sets forth detailed research on the feasibility of treatment strategies to incorporate heavy metals into structural frameworks; this paper also compares common methods and advanced characterization techniques for identifying metal stabilization mechanisms. Furthermore, this review analyses the typical hosting structures for heavy metal contaminants and metal incorporation behavior, highlighting the importance of structural features on metal speciation and immobilization efficiency. Lastly, this paper systematically summarizes key factors (i.e., intrinsic properties and external conditions) affecting metal incorporation behavior. Drawing on these impactful findings, the paper discusses future directions in the design of waste forms that efficiently, effectively treat heavy metal contaminants. By examining tailored composition-structure-property relationships in metal immobilization strategies, this review reveals possible solutions for crucial challenges in waste treatment and enhances the development of structural incorporation strategies for heavy metal immobilization in environmental applications.

Self-consumed strategy to reuse cathode residue for Zn stabilization in spent batteries: Structural properties and metal stabilization effect.

Due to ecotoxicity, zinc (Zn) as a heavy metal from electronic waste (e-waste) has been a source of pollution to soil and water for several decades. This study proposes a solution to this serious environmental problem via a self-consumed strategy to stabilize Zn in anode residues. This unique method uses cathode residues from spent zinc-manganese oxide (Zn-Mn) batteries as a stabilized matrix via thermal treatment. More specifically, the strategy incorporates zinc metal into a chemically durable matrix comprised of a lattice of AB2O4 compounds. Results demonstrate that 5-20 wt% of anode residue were fully incorporated into the cathode residue to form a Mn3-xZnxO4 solid solution after sintering at 1300 ℃ for 3 h. The lattice parameters of the Mn3-xZnxO4 solid solution reveal an approximately linear decreasing evolution with the addition of anode residue. To determine the occupancy of Zn in the crystal structure of the products, we used Raman and Rietveld refinement processes; the results reveal that Mn2+ in the 4a site was gradually replaced by Zn2+. We then used a prolonged toxicity leaching procedure to evaluate the Zn stabilization effect after phase transformation; this showed that the Zn leachability of sintered anode-doped cathode sample was over 40 folds lower than that of untreated anode residue. Therefore, this study presents an economical and effective strategy for mitigating the presence of heavy metal pollutants derived from e-waste.

UiO66-Derived Catalyst for Low Temperature Catalytic Reduction of NO with NH3.

Diesel exhaust emissions are major outdoor air pollutants. Reducing the emission of NOx by diesel commercial vehicles and related machineries is at present a great challenge. In this study, we synthesize a catalyst for low-temperature catalytic reduction of NO using calcinated UiO-66(Zr) as a host for the doping of cerium, manganese, and titanium by the incipient wetness impregnation, followed by the dispersion of 1.0 wt % platinum. A solid solution of Ce0.15Zr0.54Mn0.11Ti0.20O2/1.0Pt (CZMTO/Pt) is synthesized as evident by the structural characterizations. The catalyst demonstrates significant NO reduction in the laboratory due to the synergistic effect of various elements, with NO conversion above 80% at 160 °C.

Incorporation of lead into pyromorphite: Effect of anion replacement on lead stabilization.

Previous studies demonstrate that the leaching of heavy metals in unreliable waste forms causes serious environmental pollution and health concerns. Thus, research is focused on identifying an effective, safe strategy for disposing of metal-laden solid waste such as lead (Pb). This study evaluated the effect of anion replacement in the structure of pyromorphite (Pb10(PO4)6Cl2, a common mineral phase for Pb sequestering) on Pb stabilization. Phosphate (PO43-) at the tetrahedral pyromorphite site was simultaneously replaced by silicate (SiO44-) and sulphate (SO42-) in a controlled thermal treatment. The lattice expanded with the incorporation of additional SiO44- and SO42-. Furthermore, the unit cell parameters of the solid solutions evolved linearly with an increase in the substitution degree (x in Pb10(SiO4)x(SO4)x(PO4)(6-2x)Cl2). This research also demonstrated that Pb distributed into amorphous in a PO43--deficient matrix, while asisite (Pb7SiO8Cl2) was formed when the matrix was dominated by SiO44- and SO42-. The leaching results showed the isomorphous substitution in the target system rendered the products less durable towards acidic attack. Moreover, the fully isomorphous-substituted product (x = 3) showed more than two orders of magnitude lower leaching resistance than the PO43--rich phase (x = 0). The lattice expansion, resulting from the isomorphous substitution, suggested that a lower dissolution energy was required in a PO43--deficient matrix. The leaching kinetics pointed to a product with a lower apparent activation energy in the leaching process. The findings of this study provide unique insight into the design and optimization of waste forms for the immobilization of heavy metals.

Constructing phase boundary in AgNbO3 antiferroelectrics: pathway simultaneously achieving high energy density and efficiency.

Dielectric capacitors with high energy storage density (Wrec) and efficiency (η) are in great demand for high/pulsed power electronic systems, but the state-of-the-art lead-free dielectric materials are facing the challenge of increasing one parameter at the cost of the other. Herein, we report that high Wrec of 6.3 J cm-3 with η of 90% can be simultaneously achieved by constructing a room temperature M2-M3 phase boundary in (1-x)AgNbO3-xAgTaO3 solid solution system. The designed material exhibits high energy storage stability over a wide temperature range of 20-150 °C and excellent cycling reliability up to 106 cycles. All these merits achieved in the studied solid solution are attributed to the unique relaxor antiferroelectric features relevant to the local structure heterogeneity and antiferroelectric ordering, being confirmed by scanning transmission electron microscopy and synchrotron X-ray diffraction. This work provides a good paradigm for developing new lead-free dielectrics for high-power energy storage applications.

Effectively immobilizing lead through a melanotekite structure using low-temperature glass-ceramic sintering.

This work evaluated the feasibility of using low-temperature thermal immobilization based on the reaction mechanism forming the melanotekite (Pb2Fe2Si2O9) crystal phase to stabilize lead (Pb) containing waste. X-ray diffraction demonstrated that Pb could be incorporated into the melanotekite structure at easily attainable treatment temperatures (less than 500 °C) by magnetite and SiO2 precursors. The γ-Fe2O3 intermediate was found to play a key role in initializing melanotekite crystallization at a much lower temperature than that in traditional thermal immobilization techniques. Although a higher sintering temperature may increase Pb incorporation efficiency, amorphization occurred at temperatures higher than 950 °C. In addition, Pb was found to partition more in the amorphous phase of the SiO2-rich matrix. The results of the prolonged toxicity characteristic leaching procedure revealed a substantial improvement in the acid resistance of the targeted crystallized product sintered at 850 °C compared with the amorphous product and the other oxide products. The results of batch adsorption and subsequent thermal treatment verified the possibility of using the melanotekite structure to stabilize aqueous Pb with the Fe3O4@SiO2 residue. The study demonstrated that the melanotekite structure can be used to immobilize both solid and aqueous Pb through low-temperature thermal stabilization.

Evaluation on the stabilization of Zn/Ni/Cu in spinel forms: Low-cost red mud as an effective precursor.

Red mud, which is from the aluminum industry, is a potentially under-utilized resource. Technological processes for using low-cost red mud as an alternative precursor for detoxifying metal pollutants urgently need to be developed. In this study, we systematically investigated the feasibility of using red mud to detoxify metal-containing wastes (e.g., fly ash) via the formation of preferable crystalline phases. To understand the mechanism of metal detoxification by red mud, CuO, NiO, and ZnO were blended with red mud at different weight ratios and the mixtures were then subjected to ceramic-sintering. After sintering, the X-ray diffraction results revealed that all of the metals (i.e., Cu, Ni, and Zn) were able to be crystallographically incorporated into spinel lattices. Sintering the red mud at 1100 °C for 3 h effectively converted the metals into spinels. The mixing weight ratios strongly affected the efficiency of the metal incorporation. The red mud was able to incorporate 15 wt% of metal oxides. The incorporation mechanisms mainly occurred between the metal oxide(s) and hematite. Modified TCLP tests were conducted to further evaluate the metal stabilization performance of the red mud, which demonstrated the leachabilities of ZnO and the sintered red mud + ZnO product. The concentration of leached metal was substantially reduced after the incorporation process, thus demonstrating that red mud can be successfully used to detoxify metals. The results of this study reveal that waste red mud can be feasibly reused as a promising waste-to-resource strategy for stabilizing heavy metal wastes.

Evaluation of the effectiveness of Cd stabilization by a low-temperature sintering process with kaolinite/mullite addition.

This study first examined the phase transformation in the reactive sintering systems of cadmium-laden industrial sludge and Al-Si-rich precursors with different Cd/Al/Si molar ratios under various temperatures. X-ray diffraction results indicated that the Cd started to be incorporated at 750 °C by kaolinite or mullite (calcined from kaolinite). Three hours of processing at 950 °C can effectively incorporate Cd into Cd-Al-Si or Cd-Si materials. The amount of CdO in the reactive systems had significant influences on the Cd incorporation behavior into crystalline phases. With a small amount of CdO, product phase CdAl2Si2O8 dominated in the systems. Systems with considerable CdO produced notable amounts of Cd2SiO4 and Cd3SiO5. The production of Cd2SiO4 and Cd3SiO5 from CdO + mullite was more significant than that using kaolinite due to the preferred reaction between CdO and SiO2. To assess the effect of metal stabilization, single-phase products that host Cd (namely, CdAl2Si2O8, Cd2SiO4, and Cd3SiO5) were obtained, maintained at pH 4.0, and subjected to a constant-pH leaching test (CPLT) for 120 min. CPLT results evidently indicated that these phases were remarkably resistant to substantial acid (nitric acid) attack; the leaching behavior of CdAl2Si2O8 was incongruent dissolution. Finally, cadmium can be effectively incorporated into CdAl2Si2O8, Cd2SiO4, or Cd3SiO5 by using sludge ash from a secondary sewage treatment works, suggesting that precursors enriched with Al and Si can be promising materials in a cleaner production process for treating cadmium-laden industrial sludge.

Cu2O-promoted degradation of sulfamethoxazole by α-Fe2O3-catalyzed peroxymonosulfate under circumneutral conditions: synergistic effect, Cu/Fe ratios, and mechanisms.

To promote the application of iron oxides in sulfate radical-based advanced oxidation processes, a convenient approach using Cu2O as a catalyst additive was proposed. Composite catalysts based on α-Fe2O3 (CTX%Cu2O, X = 1, 2.5, 5, and 10) were prepared for peroxymonosulfate (PMS) activation, and sulfamethoxazole was used as a model pollutant to probe the catalytic reactivity. The results show that a synergistic catalytic effect exists between Cu2O and α-Fe2O3, which was explained by the promoted reduction of Fe(III) by Cu(I). Iron K-edge X-ray absorption spectroscopy investigations indicated that the promoted reduction probably occurred with PMS acting as a ligand that bridges the redox centers of Cu(I) and Fe(III). The weight ratio between Cu2O and α-Fe2O3 influenced the degradation of sulfamethoxazole, and the optimal ratio depended on the dosage of PMS and catalysts. With 40 mg L-1 PMS and 0.6 g L-1 catalyst, a pseudo-first-order constant of ∼0.019 min-1 was achieved for CT2.5%Cu2O, whereas only 0.004 min-1 was realized for α-Fe2O3. Nearly complete degradation of the sulfamethoxazole was achieved within 180 min under the conditions of 40 mg L-1 PMS, 0.4 g L-1 CT2.5%Cu2O, and pH 6.8. In contrast, less than 20% degradation was realized with α-Fe2O3 under similar conditions. The CT2.5%Cu2O catalyst had the best stoichiometric efficiency of PMS (0.317), which was 4.5 and 5.8 times higher than those of Cu2O (0.070) and α-Fe2O3 (0.054), respectively. On the basis of the products identified, the cleavage of the S-N bond was proposed as a major pathway for the degradation of sulfamethoxazole.