Chlorophenols breakdown by a sequential hydrodechlorination-oxidation treatment with a magnetic Pd-Fe/γ-Al2O3 catalyst

Catalytic detoxification of mitoxantrone by graphitic carbon nitride (g-C3N4) supported Fe/Pd bimetallic nanoparticles

The overuse of antibiotics and antitumor drugs has resulted in more and more extensive pollution of water bodies with organic drugs, causing detrimental ecological effects, which have attracted attention towards effective and sustainable methods for antibiotics and antitumor drug degradation. Here, the hybrid nanomaterial (g-C3N4@Fe/Pd) was synthesized and used to remove a kind of both an antibiotic and antitumor drug named mitoxantrone (MTX) with 92.0% removal efficiency, and the MTX removal capacity is 450 mg/g. After exposing to the hybrid material the MTX aqueous solution changed color from dark blue to lighter progressively, and LC-UV results of residual solutions show that a new peak at 3.0 min (MTX: 13.2 min) after removal by g-C3N4@Fe/Pd appears, with the simultaneous detection of intermediate products indicating that g-C3N4@Fe/Pd indeed degrades MTX. Detailed mass spectrometric analysis suggests that the nuclear mass ratio decreased from 445.2 (M+1H) to 126.0 (M+1H), 169.1 (M+1H), 239.2 (M+1H), 267.3 (M+1H), 285.2 (M+1H), 371.4 (M+1H) and 415.2 (M+1H), and the maximum proportion (5.63%) substance of all degradation products (126.0 (M+1H)) is 40-100 times less toxic than MTX. A mechanism for the removal and degradation of mitoxantrone was proposed. Besides, actual water experiments confirmed that the maximum removal capacity of MTX by g-C3N4@Fe/Pd is up to 492.4 mg/g (0.02 g/L, 10 ppm).

A comprehensive review of chlorophenols: Fate, toxicology and its treatment

Chlorophenols represent one of the most abundant families of toxic pollutants emerging from various industrial manufacturing units. The toxicity of these chloroderivatives is proportional to the number and position of chlorine atoms on the benzene ring. In the aquatic environment, these pollutants accumulate in the tissues of living organisms, primarily in fishes, inducing mortality at an early embryonic stage. Contemplating the behaviour of such xenobiotics and their prevalence in different environmental components, it is crucial to understand the methods used to remove/degrade the chlorophenol from contaminated environment. The current review describes the different treatment methods and their mechanism towards the degradation of these pollutants. Both abiotic and biotic methods are investigated for the removal of chlorophenols. Chlorophenols are either degraded through photochemical reactions in the natural environment, or microbes, the most diverse communities on earth, perform various metabolic functions to detoxify the environment. Biological treatment is a slow process because of the more complex and stable structure of pollutants. Advanced Oxidation Processes are effective in degrading such organics with enhanced rate and efficiency. Based on their ability to generate hydroxyl radicals, source of energy, catalyst type, etc., different processes such as sonication, ozonation, photocatalysis, and Fenton's process are discussed for the treatment or remediation efficiency towards the degradation of chlorophenols. The review entails both advantages and limitations of treatment methods. The study also focuses on reclamation of chlorophenol-contaminated sites. Different remediation methods are discussed to restore the degraded ecosystem back in its natural condition.

Novel VUV/g-C3N4 system with high adaptability to varied environmental conditions and outstanding degradation capacity for chlorophenols

Given the limitations of conventional vacuum ultraviolet (VUV) systems, a novel vacuum ultraviolet/graphite carbon nitride (VUV/g-C₃N₄) system with high adaptability to varying environmental conditions was developed. Compared with conventional VUV and UV/g-C₃N₄ systems, the VUV/g-C₃N₄ system demonstrates a much higher ability for the efficient degradation of chlorophenols (CPs). In particular, the VUV/g-C₃N₄ system exhibits outstanding performance even at low pH and high concentrations of humic acid and SO₄^2-. Alkaline conditions and the presence of HCO₃^- can further promote CP removal. In addition, the feasibility of the VUV/g-C₃N₄ system was verified by its stable operation in both river water and tap water. Unlike conventional photochemical systems relying on •OH, the dominant reactive species for CP degradation by the VUV/g-C₃N₄ system was identified to be •O₂^-. This study conclusively provided a novel system for the efficient photocatalytic treatment of pollutants.

Bibliometric analysis of advanced oxidation processes (AOPs) in wastewater treatment: global and Ibero-American research trends

Advanced oxidation processes (AOPs) constitute a developing area of particular interest for researchers in different fields due to their broad range of applications. However, there are few studies dedicated to the bibliometric analysis of AOPs. Hence, a systematic literature review of research publications (research articles, review articles, and book chapters) from 1980 to 2018 was carried out to visualize and evaluate research trends on AOPs around the world and, especially in Ibero-America (IA), on the field of wastewater treatment. Using the most extensive databases in literature search, Scopus and Web of Science (WoS), which encompass 95% of the publications in the world, a total of 18,751 records were retrieved by limiting the search results to words associated with AOPs in the titles, keyword, and abstracts. Raw data were manually organized and filtered, standardizing authors and institution names, publication titles, and keywords for the purpose of eliminating double-counted entries. Similarly, homonymous authors and institutions were identified for all records retrieved. The bibliometric dataset was processed using the VantagePoint software. The research trends visualized about AOPs were as follows: number of publications per triennium, publications by country, participation by continent, most important journals and authors, most referenced institutions, global network of co-authors, and keywords network visualization, highlighting the Ibero-American contribution to global research.

Synthesis and catalytic utilization of bimetallic systems for wastewater remediation: A review

The environment is affected by agricultural, domestic, and industrial activities that lead to drastic problems such as global warming and wastewater generation. Wastewater pollution is of public concern, making the treatment of persistent pollutants in water and wastewater highly imperative. Several conventional treatment technologies (physicochemical processes, biological degradation, and oxidative processes) have been applied to water and wastewater remediation, but each has numerous limitations. To address this issue, treatment using bimetallic systems has been extensively studied. This study reviews existing research on various synthesis methods for the preparation of bimetallic catalysts and their catalytic application to the treatment of organic (dyes, phenol and its derivatives, and chlorinated organic compounds) and inorganic pollutants (nitrate and hexavalent chromium) from water and wastewater. The reaction mechanisms, removal efficiencies, operating conditions, and research progress are also presented. The results reveal that Fe-based bimetallic catalysts are one of the most efficient heterogeneous catalysts for the treatment of organic and inorganic contamination. Furthermore, the roles and performances of bimetallic catalysts in the removal of these environmental contaminants are different.

Screening of zero valent mono/bimetallic catalysts and recommendation of Raney Ni (without reducing agent) for dechlorination of 4-chlorophenol

Chlorophenol (CP) is considered as environmentally hazardous material due to its acute toxicity, persistent nature and strong bioaccumulation. The dechlorination of 4-CP was investigated by using various catalysts such as bimetallic (Fe⁰/Cu⁰, Al⁰/Fe⁰), Pd/C, Raney Ni and Fe⁰ at room temperature. Among the catalysts studied, Raney Ni proved to be very economical and efficient catalyst that worked without the use of an external reducing agent. The dechlorination of 4-CP by Raney Ni was therefore further explored. Complete dechlorination of 4-CP (30 mg L^-1) was achieved in 6 h at an optimum Raney Ni catalyst loading of 3 g L^-1. The effect of triethylamine (TEA) and tripropylamine (TPA) was also investigated and it was observed that 100% dechlorination is possible in presence of 45 mg L^-1 of TEA. The kinetics of dechlorination of 4-CP was investigated and found to be first order with a rate constant of 0.017 min^-1 at 50 ^οC, and it enhances to 0.109 min^-1 with addition of TEA. In the absence of a reducing agent, acidic to neutral pH favors dechlorination of 4-CP. The final product of dechlorination was estimated to be phenol by performing HPLC, LCMS and NMR analysis. Based on the results, a probable dechlorination mechanism of 4-CP is also proposed. It can be concluded that the catalytic hydrodechlorination is an effective and economical technique for dechlorination of 4-CP and it has a potential for the dechlorination of other toxic derivatives of chlorinated aromatics.

Effect of the supports on catalytic activity of Pd catalysts for liquid-phase hydrodechlorination/hydrogenation reaction

Carbon nanotubes (CNTs), activated carbon (AC), graphene, and aluminum oxide (Al₂O₃) supported 5% Pd catalysts were prepared by the conventional impregnation method, and catalytic activity was tested in the hydrogenation of 4-chlorophenol (4-CP) and nitrobenzene (NB) under ambient conditions (313 K and atmospheric pressure). It was found that catalytic activity was greatly affected by the supports. Moreover, Pd/CNTs catalyst exhibited much higher catalytic activity than the other three supported Pd catalysts. The mechanism of this phenomenon was studied through catalyst characterization (ICP-MS, Brunauer-Emmett-Teller [BET], TEM, and SEM). It was found that the mean particle size of Pd nanoparticles for Pd/CNTs (4.3 nm) was smaller than that for Pd/AC (6.9 nm), Pd/Al₂O₃ (5.0 nm), and Pd/graphene (5.2 nm). Moreover, the actual loading amounts of Pd and BET surface areas were not the main reasons for the different catalytic activity of the four supported Pd catalysts. Above all, the smaller Pd particles of Pd/CNTs enabled the Pd/CNTs catalyst to exhibit much higher catalytic activity for the hydrogenation reactions.

Well-dispersed Pd nanoparticles on porous ZnO nanoplates via surface ion exchange for chlorobenzene-selective sensor

The extensive use of chlorobenzene in chemical, pharmaceutical, and agrochemical industries poses a severe health hazard to human beings, because it is highly toxic. The detection of chlorobenzene by metal oxide gas sensors is difficult, owing to its chemically inert molecular structure. In this study, well-dispersed Pd nanoparticles were deposited on porous ZnO nanoplates via surface ion exchange, followed by H₂ reduction. The preparation process effectively prevented the aggregation and uncontrollable growth of Pd particles. A gas-sensing test was conducted, and the modification of size-controlled Pd nanoparticles was found to effectively enhance the sensing properties of porous ZnO nanoplates to chlorobenzene over 300 °C (higher sensitivity at a low operating temperature). At 440 °C, 5% Pd@ZnO sensor showed a drastic increase in response by nearly 4.5-fold, as well as excellent sensing selectivity to chlorobenzene. Its repeatability and stability were acceptable. As known, Pd nanocatalysts contribute to the oxidation of chlorinated aromatic compounds. Pd@ZnO sensors generated more catalytic sites and oxygen species (confirmed by XPS), thus enhancing chlorobenzene oxidation and improving the sensitivity of ZnO-based gas sensors.

Well-dispersed and size-controlled Pd nanocatalysts were deposited on porous ZnO nanoplates via surface ion exchange for enhanced and selective chlorobenzene-sensor.

Comparative study on catalytic hydrodehalogenation of halogenated aromatic compounds over Pd/C and Raney Ni catalysts

Catalytic hydrodehalogenation (HDH) has proved to be an efficient approach to dispose halogenated aromatic compounds (HACs). Liquid-phase HDH of single and mixed halobenzenes/4-halophenols with H₂ over 5% Pd/C and Raney Ni catalyst are investigated and compared. For liquid-phase HDH of single HACs, hydrogenolytic scission reactivity of C-X bonds decreases in order of C-Br > C-Cl > C-I > C-F over Pd/C catalyst, and in order of C-I > C-Br > C-Cl > C-F over Raney Ni catalyst. To clarify the reason why hydrogenolytic scission reactivity of C-X bonds over Pd/C and Raney Ni catalysts exhibits different trends, liquid-phase HDH of mixed HACs over Pd/C and Raney Ni catalysts were studied, and catalysts are characterized by SEM, EDX, and XRD techniques. It was found that the high adsorption of iodoarenes on Pd/C catalyst caused the HDH reactivity of iodoarenes to be lower than that of chloroarenes and bromoarenes in the HDH of single HACs. Moreover, the adsorption of in situ produced iodine ion (I⁻) to catalyst surface would result in the decline of catalytic activity, which might be the main reason why the HDH reactivity of HACs in the presence of NaI is rather low.

A highly active bimetallic oxide catalyst supported on γ-Al2O3/TiO2 for catalytic wet peroxide oxidation of quinoline solutions under microwave irradiation

A new heterogeneous wet oxidation catalyst, Cu–Ni bimetallic oxides supported on γ-Al₂O₃/TiO₂, was synthesized using a wet impregnation method

Treatment of halogenated phenolic compounds by sequential tri-metal reduction and laccase-catalytic oxidation

Halogenated phenolic compounds (HPCs) are exerting negative effects on human beings and ecological health. Zero-valence metal reduction can dehalogenate HPCs rapidly but cannot mineralize them. Enzymatic catalysis can oxidize phenolic compounds but fails to dehalogenate efficiently, and sometimes even produces more toxic products. In this study, [Fe|Ni|Cu] tri-metallic reduction (TMR) and laccase-catalytic oxidation (LCO) processes were combined to sequentially remove HPCs, including triclosan, tetrabromobisphenol A, and 2-bromo-4-fluorophenol in water. The kinetics, pH and temperature dependences of TMR and LCO were obtained. The detailed TMR, LCO, and TMR-LCO transformation pathways of three HPCs were well described based on the identification of intermediate products and frontier molecular orbitals (FMOs) theory. The results showed that the two-stage process worked synergically: TMR that reductively dehalogenated HPCs followed by LCO that completely removed dehalogenated products. TMR was proven to not only improve biodegradability of HPCs but also reduce the yield of potential carcinogenic by-products. Furthermore, a TMR-LCO flow reactor was assembled and launched for 256 h, during which >95% HPCs and >75% TOC were removed. Meanwhile, monitored by microorganism indicators, 83.2%-92.7% acute toxicity of HPCs was eliminated, and the genotoxicity, produced by LCO, was also avoided by using TMR as pretreatment process.

Remediation of DDTr contaminated soil by the combination of solvent extraction and catalytic hydrodechlorination

A combination technique for remediation of DDT and its metabolites (DDTr) contaminated soil based on successive steps of solvent extraction, followed by catalytic hydrodechlorination (HDC) was studied.