Degradation Of Contaminants Research Articles

Strontium doping-tailored inverse spinel phase in cobalt chromite with enhanced photo-degradation of ofloxacin

Spinel materials are attractive to photocatalytic degradation of contaminants. In this study, strontium (Sr) doped spinel cobalt chromite (CoCr2O4) was synthesized by solution combustion method and characterized using techniques such as X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and electrochemical impedance spectroscopy (EIS). 30 -50 nm-cubic CoCr2O4 nanocrystals were obtained, and phase transitions of CoO6→CoO4 and CrO4→CrO6 occurred as the Sr doping content increased until 0.6 % Sr doped sample displayed an inverse spinel phase. The modifications in composition and structure induced the co-existence of multivalent states for Co and Cr, which in turn changed the optical, complex impedance, and magnetic spin state of CoCr2O4. The 0.6 % Sr-doped sample showed the highest photocatalytic efficiency of 93 % due to enhanced optical absorption, reduced energy band gap, oxygen vacancies formation, and a high spin state of Co. The XRD structure and photocatalytic activity remained stable even after five cycles without any leakage of metal elements. The degradation pathway and Mott-Schottky curves were employed to elucidate the mechanism behind this enhancement. The strategy employed in this study proved effective, and the synthesized materials show promise for the photocatalytic degradation of contaminants.

Doped Cu0 and sulfidation induced transition from R-O• to •OH in peracetic acid activation by sulfidated nano zero-valent iron-copper

Peracetic acid (PAA) has emerged as a new effective oxidant for various contaminants degradation through advanced oxidation process (AOP). In this study, sulfidated nano zero-valent iron-copper (S-nZVIC) with low Cu doping and sulfidation was synthesized for PAA activation, resulting in more efficient degradation of sulfamethoxazole (SMX, 20 μM) and other contaminants using a low dose of catalyst (0.05 g/L) and oxidant (100 μM). The characterization results suggested that S-nZVIC presented a more uniform size and distribution with fewer metal oxides, as the agglomeration and oxidation were inhibited. More significantly, doped Cu0 and sulfidation significantly enhanced the generation and contribution of •OH but decreased that of R-O• in S-nZVIC/PAA/SMX system compared with that of nZVIC and S-nZVI, accounting for the relatively high degradation efficiency of 97.7% in S-nZVIC/PAA/SMX system compared with 85.7% and 78.9% in nZVIC/PAA/SMX and S-nZVI/PAA/SMX system, respectively. The mechanisms underlying these changes were that (i) doped Cu° could promote the regeneration of Fe(Ⅱ) for strengthened PAA activation through mediating Fe(Ⅱ)/Fe(Ⅲ) cycle by Cu(Ⅰ)/Cu(Ⅱ) cycle; (ii) S species might consume part of R-O•, resulting in a decreased contribution of R-O• in SMX degradation; (iii) sulfidation increased the electrical conductivity, thus facilitating the electron transfer from S-nZVIC to PAA. Consequently, the dominant reactive oxygen species transited from R-O• to •OH to degrade SMX more efficiently. The degradation pathways, intermediate products and toxicity were further analyzed through density functional theory (DFT) calculations, liquid chromatography-mass spectrometry (LC-MS) and T.E.S.T software analysis, which proved the environmental friendliness of this process. In addition, S-nZVIC exhibited high stability, recyclability and degradation efficiency over a wide pH range (3.0∼9.0). This work provides a new insight into the rational design and modification of nano zero-valent metals for efficient wastewater treatment through adjusting the dominant reactive oxygen species (ROS) into the more active free radicals.

Photocatalytic Degradation of Maxilon Dye Pollutants using Nano‐Architecture Functional Materials: A Review

AbstractThe most essential task in the twenty‐first century is to fight the alarming growing pollution in the aquatic body in which effluent of one of the most colouring dye categories called maxilon dye is a major contributor. This review thus specifically focuses on the use of nanoparticles (NPs) for photocatalytic degradation of maxilon dye contaminants in water bodies. The work empirically presented the performance evaluation of NPs in degrading maxilon dyes under light irradiation alongside the underlying operational photocatalytic degradation mechanism. The stability of NPs was also critically analyzed by looking at the regenerability and reusability of expended NPs. From the study, it was discovered that ⋅OH and O2⋅ played a vital role in the genesis of the oxidizing capacity of NPs for the photocatalytic breakdown of maxilon dye. Moreover, it was found that the degradation performance of most NPs is greater than 80 % and the shortest degradation period is < 1 hour with pseudo‐first‐order (PFO) being the most common kinetic best‐fit to describe the adsorption process that occurred shortly before and during the degradation operation. At the end, knowledge gaps were identified in the area of regenerability, the lifecycle analyses of nano‐photocatalyst fabrication and utilization, cost analysis for industrial scale‐up, maxilon dye ecotoxicological study, and degradation pathways. The findings of this study can open up insightful innovation for readers and industries that are interested in pursuing zero water insecurity.

Kinetic model-based optimization in electro-activated sulfite system for carbamazepine degradation: Aeration and multiple dosages of sulfite

Electro-activated sulfite system (E-SO32−) was an emerging advanced oxidation technology, but its kinetics and process optimization have been overlooked. This study developed a first-principle kinetic model to investigate carbamazepine (CBZ) degradation and optimized this process by aeration and multiple dosages of SO32−. A low aeration rate (140 mL/min) remarkably accelerated sulfate radical (SO4•−) generation because of the enhanced rate of sulfite radical (SO3•−) reacting with oxygen. Thus, the degradation efficiency of CBZ improved from 71 % to 84 % and the electrical energy per order (EE/O) decreased from 4.55 to 2.32 kWh/m3/order at current density of 103 A/m2 and initial dosage of SO32− of 4 mM. However, further increasing the aeration rate diminished the enhancement of SO4•− generation rate due to the limited SO3•− generation, and excessive aeration resulted in decreased degradation efficiency and increased cost of aeration due to the direct oxidation of SO32− by oxygen. Consequently, matching of SO32− concentration, current density and aeration rate was crucial to maximize the generation rate of SO4•−. The most optimal strategy was at current density of 75 A/m2, aeration rate of 100 mL/min and SO32− concentration of 1.1 mM with multiple dosages. 95 % of CBZ was removed in 20 min, 18 % higher than that in single dosage. Finally, the optimal strategy for CBZ degradation was successfully applied in different water matrixes and real wastewater and well predicted by the kinetic model. Furthermore, degradation pathways of CBZ, including hydroxylation and deamidation, were elucidated from density functional theory and LC-MS detection. The toxicity of most intermediates decreased, while some intermediates possessed higher toxicity than CBZ. Overall, the firstly proposed combined strategy of aeration and multiple dosages of SO32− significantly facilitated the application of E-SO32− system in contaminants degradation.

Surface coordination induced a quasi p-n junction for efficient visible light driven degradation of tetracycline over hydroxyapatite

The removal of antibiotics from aquatic solutions remains a global environmental challenge. In this work, the photocatalytic removal of a typical antibiotic-tetracycline (TC) using hydroxyapatite (HAp) as a catalyst was investigated. It was impressive that TC could be efficiently degraded by HAp under visible light irradiation, even though both HAp and TC exhibited poor harvesting in visible light region. The experimental and theoretical explorations were undertaken to thoroughly investigate the underlying mechanism of visible light degradation of TC over HAp. The results indicated that the formed TC-HAp complexes via surface coordination played an important role as photosensitizers for the visible light response. Together with the formation of a quasi p-n junction via band alignment, the photogenerated electrons in the highest unoccupied molecular orbital (HOMO) of TC-HAp were excited to the lowest unoccupied molecular orbital (LUMO) and subsequently migrated to the conduction band of HAp to achieve the efficient charge separation. Superoxide radicals and holes were found to be the major active species for TC degradation. The toxicity evaluation showed that TC could be transferred to the lower toxic intermediates, and deep oxidation with prolonged reaction time was necessary to eliminate the toxicity of TC. This work demonstrates the surface coordination with subsequent quasi p-n junction mechanism of TC degradation over HAp under visible light, which will stimulate us to explore new efficient photocatalytic systems for the degradation of various contaminants.

A bifunctional wood membrane modified by MoS2/covalent organic framework heterojunctions for effective solar-driven water evaporation and contaminant degradation

A bifunctional wood membrane modified by MoS2/covalent organic framework heterojunctions for effective solar-driven water evaporation and contaminant degradation

Mo-modified BiOI0.5Cl0.5 composites preparation for antibiotic removal

Photocatalytic technology has the advantages of high efficiency, mild reaction conditions, low cost, and minimal secondary contamination in antibiotic degradation. Bismuth oxyhalides(BiOX) has garnered considerable attention and application as a photocatalyst, due to its suitable band gap and light capture capability. In this study, we successfully synthesized the BiOI0.5Cl0.5 (BCI) material through hydrothermal treatment. Furthermore, Molybdenum (Mo) atoms were diffused into the composite to form Mo-doped Mo@BiOI0.5Cl0.5. Various techniques were employed to characterize the structures, chemical compositions, and morphologies of the obtained materials.The photocatalytic performance of the obtained materials was investigated, revealing that MBCI-3 exhibited superior performance in the photocatalytic degradation of contaminants. Over a span of 20 min, 100% of rhodamine B and 86.0% of tetracycline were successfully removed from water. The enhancement in photocatalytic performance can be attributed to the alteration in the band gap of the BCI complex, leading to improved light absorption, while the incorporation of Mo atoms expedites electron transfer. Finally, the role of h+ and O2•- radicals in photocatalytic degradation was verified through radical trapping experiments.

An integrated evaluation of bioenhanced in situ LNAPL dissolution

Performance evaluation of in situ bioremediation processes in the field is difficult due to uncertainty created by matrix and contaminant heterogeneity, inaccessibility to direct observation, expense of sampling, and limitations of some measurements. The goal of this research was to develop a strategy for evaluating in situ bioremediation of light nonaqueous-phase liquid (LNAPL) contamination and demonstrating the occurrence of bioenhanced LNAPL dissolution by: (1) integrating a suite of analyses into a rational evaluation strategy; and (2) demonstrating the strategy's application in intermediate-scale flow-cell (ISFC) experiments simulating an aquifer contaminated with a pool of LNAPL (naphthalene dissolved in dodecane). Two ISFCs were operated to evaluate how the monitored parameters changed between a “no bioremediation” scenario and an “intrinsic in situ bioremediation” scenario. Key was incorporating different measures of microbial activity and contaminant degradation relevant to bioremediation: contaminant loss; consumption of electron acceptors; and changes in total alkalinity, pH, dissolved total inorganic carbon, carbon-stable isotopes, microorganisms, and intermediate metabolites. These measurements were integrated via mass-flux modeling and mass-balance analyses to document that in situ biodegradation of naphthalene was strongly accelerated in the “intrinsic in situ bioremediation” scenario versus “no bioremediation.” Furthermore, the integrated strategy provided consistent evidence of bioenhancement of LNAPL dissolution through intrinsic bioremediation by a factor of approximately 2 due to the biodegradation of the naphthalene near the pool/water interface.

Insights into the Ligand Effect in β-CD@Fe3O4 Composites to Activate Peroxymonosulfate for Efficient Degradation of Pharmaceutical Contaminants: A Study Employing Density Functional Theory

This study presents a detailed investigation into the use of β-cyclodextrin (β-CD) encapsulated iron oxide nanoparticle (β-CD@Fe3O4) composites, modified with different ligands, to activate peroxymonosulfate (PMS) for the degradation of pharmaceutical contaminants, namely, diclofenac, carbamazepine, and erythromycin. The focus is on understanding the ligand effect, particularly using citric acid (CIT), polyethyleneimine (PEI), and cetyl trimethyl ammonium bromide (CTAB), on the degradation performance of these composites. Employing density functional theory (DFT) calculations, this work examines the electronic structure and charge distributions of β-CD@Fe3O4 composites, providing insights into their interaction with various pollutants. The study reveals that the β-CD@PEI@Fe3O4 composite demonstrates superior degradation efficiency due to optimal electrostatic interactions, regardless of the pollutant’s hydrophobicity. On the other hand, β-CD@CIT@Fe3O4 shows moderate efficiency, and β-CD@CTAB@Fe3O4 exhibits selective efficiency, particularly for hydrophobic compounds. These findings underscore the significant role of surface chemistry in modulating the activation of PMS and the degradation of contaminants, opening avenues for designing tailored β-CD composites for environmental remediation.

Integrated AI-driven optimization of Fenton process for the treatment of antibiotic sulfamethoxazole: Insights into mechanistic approach

Antibiotics, as a class of environmental pollutants, pose a significant challenge due to their persistent nature and resistance to easy degradation. This study delves into modeling and optimizing conventional Fenton degradation of antibiotic sulfamethoxazole (SMX) and total organic carbon (TOC) under varying levels of H2O2, Fe2+ concentration, pH, and temperature using statistical and artificial intelligence techniques including Multiple Regression Analysis (MRA), Support Vector Regression (SVR) and Artificial Neural Network (ANN). In statistical metrics, the ANN model demonstrated superior predictive accuracy compared to its counterparts, with lowest RMSE values of 0.986 and 1.173 for SMX and TOC removal, respectively. Sensitivity showcased H2O2/Fe2+ ratio, time and pH as pivotal for SMX degradation, while in simultaneous SMX and TOC reduction, fine tuning the time, pH, and temperature was essential. Leveraging a Hybrid Genetic Algorithm-Desirability Optimization approach, the trained ANN model revealed an optimal desirability of 0.941 out of 1000 solutions which yielded a 91.18% SMX degradation and 87.90% TOC removal under following specific conditions: treatment time of 48.5 min, Fe2+: 7.05 mg L−1, H2O2: 128.82 mg L−1, pH: 5.1, initial SMX: 97.6 mg L−1, and a temperature: 29.8 °C. LC/MS analysis reveals multiple intermediates with higher m/z (242, 270 and 288) and lower m/z (98, 108, 156 and 173) values identified, however no aliphatic hydrocarbon was isolated, because of the low mineralization performance of Fenton process. Furthermore, some inorganic fragments like NH4+ and NO3− were also determined in solution. This comprehensive research enriches AI modeling for intricate Fenton-based contaminant degradation, advancing sustainable antibiotic removal strategies.

Core–shell CoN@Co ultra-stable nanoparticles on biochar for contamination remediation in water and soil

Nanomaterials have been extensively employed in various applications over the past several decades, however, the stability of functional nanoparticle catalysts (NPCs) for effective degradation of organic contaminants remains a significant challenge. Herein, we present a cost-effective biochar loaded uniformly dispersed ultra-stable Co nanoparticles with an average diameter of 8 nm as a highly efficient peroxymonosulfate (PMS) activation catalyst. The reactive radicals produced from the catalyst/PMS system are able to degrade several model organic pollutants of environmental and public health concerns, including trichlorobiphenyl, bisphenol A and diethyl phthalate, with less pH limitation and Co2+ leaching. Mechanism investigation demonstrates that the CoN plays the key role in the catalyst stability and PMS activation via acid resistance and electron bridging effects, respectively. Meanwhile, the incorporation of nitrogen (N) and sulfur (S) atoms within the substrate is considered to bolster the adhesion strength between metal nanoparticles and the carbon matrix via strong metal-support interaction. The catalyst was further applied in practical treatment of water and soil polluted by organic pollutants, exhibiting a satisfactory degradation efficiency (> 90% in 60 min) for environmental applications.

Interfacial OOH* mediated Fe(II) regeneration on the single atom Co-N-C catalyst for efficient Fenton-like processes

Fe(II) regeneration is decisive for highly efficient H2O2-based Fenton-like processes, but the role of cobalt-containing reactive sites in promoting Fe(II) regeneration was overlooked. Herein, a single atom Co-N-C catalyst was employed in Fe(II)/H2O2 system to promote the degradation of diverse organic contaminants. The EPR and quenching experiments indicated Co-N-C significantly enhanced the generation of superoxide species, and accelerated hydroxyl radical generation for pollutant degradation. The electrochemical and surface composition analyses demonstrated the enhanced H2O2 activation and Fe(III)/Fe(II) recycling on the catalyst. Furthermore, in-situ Raman characterization with shell-isolated gold nanoparticles was employed to visualize the interfacial reactive intermediates and their time-resolved interaction. The accumulation of interfacial CoOOH* was confirmed when Co-N-C activated H2O2 alone, but it rapidly transformed into FeOOH* upon Fe(II) addition. Besides, the temporal variation of OOH* intermediates and the relative intensity of Co(III)-O and Co(IV)=O peaks depicted the dynamic interaction of reactive intermediates along the H2O2 consumption. With this basis, we proposed a mechanism of interfacial OOH* mediated Fe(II) regeneration, which overcame the kinetical limitation of Fe(II)/H2O2 system. Therefore, this study provided a primary effort to elucidate the overlooked role of interfacial CoOOH* in the Fenton-like processes, which may inspire the design of more efficient catalysts.

Metal-Free Activated Carbon Catalytic for Degradation of Organic Contaminants by Peroxydisulfate Activation

Green chemistry has become trending recently, and the discovery of environmentally friendly catalysts is mandatory. Activated carbons (ACs) are one of the most environmentally friendly yet cheap materials that have the potential for catalyst application. Three commercially available ACs from Pancasari, Norit, and Chemical Supply were used as metal-free catalysts for advanced oxidation process (AOP) phenol removal in water in the presence of oxidants peroxydisulfate (PDS), and hydrogen peroxide (H2O2). It was found that ACs were effective to be used as catalysts for activating those oxidants to oxidize phenol in AOP reactions. In this study, the surface area of the catalyst significantly improved the phenol removal efficiency. ACs Pancasari (ACP) with the highest surface area has the best degradation performance of phenol removal with up to 99% removal efficiency in 60 minutes under the condition of [phenol] = 30 mg L-1, [ACP] = 0.2 g L-1, [PDS] = 3.3 mmol L-1, and T = 25oC. it was also found that the degradation process was significantly influenced by reaction temperature. Nevertheless, in this study, ACs display the potential as catalysts in the AOP process for wastewater treatments.

Surface-bound radicals enhancing detoxification of enrofloxacin during peroxymonosulfate oxidation: Activated carbon vs. alumina as catalyst carriers

Recent studies have found the presence of surface-bound radicals (Surf-R) during the heterogeneously catalyzed peroxymonosulfate (PMS), especially when the catalyst carriers possess a high adsorption capacity. However, the effects of Surf-R on the toxicity of transformation products (TPs) are still not well elucidated. In this study, Co and Mn were loaded onto commonly used carriers: activated carbon and alumina (CoMn@AC vs CoMn@Al2O3) to create comparable catalytic centers but distinct adsorption capacity, which was proved by material characterization (SEM, EDS, BET, XPS), adsorption and catalytic tests. Both images and quantitative analysis with 3D excitation-emission matrix fluorescence spectroscopy demonstrated that the reaction solutions of enrofloxacin from two catalysts composed differently when a same degradation efficiency was achieved. It was further found that the respiratory inhibition of CoMn@AC catalyzed samples was only 7–36% of the counterpart. 50 TPs were identified with UPLC-MS/MS, among which 31 TPs were possibly more toxic than enrofloxacin according to the calculation with the Toxicity Estimation Software Tool. CoMn@Al2O3 produced 14 unique toxic TPs while CoMn@AC only 4. The analysis with EPR revealed that both catalysts generated SO4•-, •OH, and 1O2; quenching tests proved a lot of Surf-R with CoMn@AC but not with CoMn@Al2O3. This study demonstrates the high potential of Surf-R to enhance the detoxification of organic contaminants during PMS oxidation and thus provides a reference for designing novel catalysts to achieve efficient contaminant degradation and detoxification.

Waste to worth: Facile preparation of CaO2 derived from oyster shells for highly efficient degradation of organic contaminants based on Fenton-like system

In recent years, CaO2 has been frequently used as a substitute for H2O2 to address the limitations of H2O2. However, commercially available CaO2 are facing the shortcomings of low purity and limited preparation conditions. Oyster shells can provide superior and abundant biomass calcium element with low cost for developing CaO2. In this work, highly purified CaO2 functional biomaterials were prepared via a facile approach derived from waste oyster shells, which were applied in a Fenton-like system to remove organic pollutants. Experimental results indicated that the oyster shells-derived CaO2 with 100% purity exhibited a greatly enhanced catalytic performance compared with other CaO2 materials in Fenton-like catalytic degradation of organic pollutants, which can be completely removed within 60 s. The high purity of CaO2 would facilitate the release of H2O2 during the Fenton-like catalytic reaction and promote the generation of more active species to oxidize pollutants. Besides, the abundant trace metal elements originated from oyster shells can further motivate the Fenton-like reaction and accelerate the degradation of pollutants, endowing oyster shells-derived CaO2 an excellent catalytic activity. Furthermore, the Fenton-like catalytic mechanism was proposed on basis of tests of radicals trapping and electron spin resonance, validating the vital roles of ⋅OH, ⋅O2– and 1O2 generated throughout the reaction process. This work not only provides a novel and low-cost approach to exploit CaO2 with highly efficient catalytic ability, but also realizes the effective resource utilization of waste shells.

Construction of a direct Z-scheme Cs3Bi2Cl9/g-C3N4 heterojunction composite for efficient photocatalytic degradation of various pollutants in water: Performance, kinetics and degradation mechanism

The use of emerging composite materials has been booming to remove environmental pollutants. The aim of this research is to develop a new composite based on Cs3Bi2Cl9 perovskite and graphitic carbon nitride (g-C3N4) to investigate the photocatalytic performance under visible light irradiation. To achieve this, we produce the Cs3Bi2Cl9/g-C3N4 heterojunctions through a simple self-assembly synthesis. The as-synthesized composites are characterized using XRD, FTIR, FESEM, TEM, BET and EDX techniques. The photocatalytic performance of Cs3Bi2Cl9/g-C3N4 is examined in the degradation of various water contaminants, including 4-nitrophenol (4-NP), tetracycline antibiotic (TC), methylene blue (MB) and methyl orange (MO). The experimental results indicate the superior photocatalytic performance of the composites in the degradation of pollutants compared to pure Cs3Bi2Cl9 and g-C3N4. The 10% Cs3Bi2Cl9/g-C3N4 composite achieves the optimal degradation efficiency of 100, 92, 98.7, and 85.1% of 4-NP, TC, MB, and MO, respectively. This superior photocatalytic activity attributes to improved optical and electrochemical properties, including enhanced absorption ability, narrowing band gap, promoted separation efficiency of photogenerated carriers, and a high redox potential, which is confirmed by UV–vis DRS, PL, EIS, and CV analyses. The 10% Cs3Bi2Cl9/g-C3N4 composite also demonstrates high photocatalytic stability after four consecutive cycles. Radical trapping tests show that superoxide radicals (•O2−), holes (h+), and hydroxyl radicals (•OH) contribute to the photocatalytic process. Based on the obtained data, a direct Z-scheme heterojunction mechanism is proposed. Overall, this research offers a new stable photocatalyst with excellent prospect for photocatalytic applications.

Enhancing photocatalytic degradation of crystal violet dye with g‐C3N4/ZnTiO3 nanocomposites synthesized via a facile approach

AbstractPhotocatalysts that exhibit exceptional performance could be further enhanced for wastewater treatment, particularly in the degradation of organic pollutants and reduction of inorganic heavy metal ions concentrations. This study employed sol–gel techniques was used to create a Type II scheme g‐C3N4/ZnTiO3 (CZT‐2, CZT‐4, and CZT‐6) photocatalyst. FT‐IR, UV‐DRS, XRD, SEM, BET, HR‐TEM, and XPS analysis were conducted to investigate the physical and chemical properties of the g‐C3N4/ZnTiO3 photocatalyst's. An investigation was conducted to evaluate the photocatalytic performance of the synthesized samples. The samples exhibit remarkable efficacy in the degradation of organic contaminants. Among them, CZT‐2 showcased superior photocatalytic performance in the solar light‐induced photodegradation of crystal violet. The photocatalytic activity of g‐C3N4/ZnTiO3 has been significantly enhanced through the establishment of a Type‐II scheme at the interface. This innovative approach efficiently facilitates the separation of photogenerated electron–hole pairs, thereby boosting the photodegradation activity. The discussion also included the chemical process between photocatalysts and crystal violet. The mechanism of the crystal violet‐photocatalyst reaction was also discussed. After undergoing five cycles of reuse, the photocatalyst that was manufactured demonstrated remarkable stability, leading to a reduction in the cost associated with wastewater treatment. The as‐synthesized g‐C3N4/ZnTiO3 composites are very safe for the environment, which suggests that the CZT‐2 composite is very good at getting rid of pollutants.

Optimization of adaptive and sustainable gold ore grinding processes for better environmental and land conditions in the small-scale gold mining sector in Indonesia

The artisanal and small-scale gold mining (ASGM) sector largely relies on mercury in gold processing, posing potential environmental contamination, health issues, and land degradation. In the villages of Tatelu and Talawaan, ASGM operations, guided by local knowledge and resources, have transitioned to using cyanide leaching for gold processing sustainably. These operations utilize andesitic stones from river deposits as grinding media in the grinding process. However, the cyanide leaching results were not optimal, with a gold recovery below 60%. This leaves significant amounts of gold in the waste, necessitating further processing and the incomplete treatment of free cyanide waste. The suboptimal gold recovery in cyanide leaching is attributed to the inadequate grain size liberation during grinding. This study optimized grinding by comparing andesitic stone grinding media with steel balls and rods. The findings indicate that to achieve a grain size of 75% passing 74 um, grinding with andesitic stones takes 4 hours, while steel rods and balls take 3 hours. For a grain size of 75% passing 44 um, grinding with andesitic stones, steel balls, and rods requires 6 hours. With more precise process parameters, locally available andesitic stones can be an effective grinding medium to optimize gold recovery. In line with optimizing gold recovery, this will enhance ASGM's revenue, encouraging the adoption of waste management practices to alleviate environmental impact, health risks, and land degradation. This aligns with the promotion of sustainable practices within the ASGM sector.

Rational Design and Synthesis of Fe-Doped Co-Based Coordination Polymer Composite Photocatalysts for the Degradation of Norfloxacin and Ciprofloxacin.

The solar light-responsive Fe-doped Co-based coordination polymer (Fe@Co-CP) photocatalyst was synthesized under mild conditions. [Co(4-padpe)(1,3-BDC)]n (Co-CP) was first constructed using mixed ligands through the hydrothermal method. Then, Fe was introduced into the Co-CP framework to achieve the enhanced photocatalytic activity. The optimal Fe@Co-CP-2 exhibited excellent catalytic degradation performance for norfloxacin and ciprofloxacin under sunlight irradiation without auxiliary oxidants, and the degradation rates were 91.25 and 92.66% in 120 min. These excellent photocatalytic properties were ascribed to the generation of the Fe-O bond, which not only enhanced the light absorption intensity but also accelerated the separation efficiency of electrons and holes, and hence significantly improved the photocatalytic property of the composites. Meanwhile, Fe@Co-CP-2 displayed excellent stability and reusability. In addition, the degradation pathways and intermediates of antibiotic molecules were effectively analyzed. The free radical scavenging experiment and ESR results confirmed that •OH, •O2-, and h+ active species were involved in the catalytic degradation reaction; the corresponding mechanisms were deeply investigated. This study provides a fresh approach for constructing Fe-doped Co-CP-based composite materials as photocatalysts for degradation of antibiotic contaminants.

Assessing the Chemical-Free Oxidation of Trace Organic Chemicals by VUV/UV as an Alternative to Conventional UV/H2O2.

Low-pressure mercury lamps with high-purity quartz can emit both vacuum-UV (VUV, 185 nm) and UV (254 nm) and are commercially available and promising for eliminating recalcitrant organic pollutants. The feasibility of VUV/UV as a chemical-free oxidation process was verified and quantitatively assessed by the concept of H2O2 equivalence (EQH2O2), at which UV/H2O2 showed the same performance as VUV/UV for the degradation of trace organic contaminants (TOrCs). Although VUV showed superior H2O activation and oxidation performance, its performance highly varied as a function of light path length (Lp) in water, while that of UV/H2O2 proportionally decreased with decreasing H2O2 dose regardless of Lp. On increasing Lp from 1.0 to 3.0 cm, the EQH2O2 of VUV/UV decreased from 0.81 to 0.22 mM H2O2. Chloride and nitrate hardly influenced UV/H2O2, but they dramatically inhibited VUV/UV. The competitive absorbance of VUV by chloride and nitrate was verified as the main reason. The inhibitory effect was partially compensated by •OH formation from the propagation reactions of chloride or nitrate VUV photolysis, which was verified by kinetic modeling in Kintecus. In water with an Lp of 2.0 cm, the EQH2O2 of VUV/UV decreased from 0.43 to 0.17 mM (60.8% decrease) on increasing the chloride concentration from 0 to 15 mM and to 0.20 mM (53.5% decrease) at 4 mM nitrate. The results of this study provide a comprehensive understanding of VUV/UV oxidation in comparison to UV/H2O2, which underscores the suitability and efficiency of chemical-free oxidation with VUV/UV.