Carbon coating enhances single-electron oxygen reduction reaction on nZVI surface for oxidative degradation of nitrobenzene

A tartaric acid (TA)-coated iron-based biochar as heterogeneous fenton catalyst for enhanced degradation of dibutyl phthalate

Iron-biochar composite is a promising catalyst in Fenton-like system for removal of organic pollutants. Nevertheless, low cycling rate of Fe(III)/Fe(II), high iron leaching and low H2O2 utilization efficiency impedes its application. Herein, a iron-based biochar (C-Fe) coated with tartaric acid (TA) was synthesized. The specific structure of inherent graphitized carbon and TA coating improved the removal efficiency of dibutyl phthalate (DBP) to 93%, promoted 2-fold increase in HO• production in H2O2 activation, improved the cycling rate of Fe(III)/Fe(II), and mitigated Fe leaching significantly. The developed HO• and 1O2 dominated Fenton-like system had an excellent pH universality and anti-interference to inorganic ions and real water matrixes. Moreover, C-Fe-TA has been shown to efficiently degrade DBP by using the dissolved oxygen in water to generate HO•. This work provided a novel insight for sustainable and efficient HO• and 1O2 generation, which motivated the development of new water treatment technology based on efficient iron-biochar catalyst.

Extensive optical and DFT studies on novel AIE active fluorescent sensor for Colorimetric and fluorometric detection of nitrobenzene in Solid, solution and vapor phase

An electron rich isophthalamide based sensor IPA has been synthesized through a simple two-step reaction, containing noteworthy aggregation induced emission (AIE) properties. Considering the significant emission with λmax at 438 nm, sensor IPA has been employed for the sensing of nitrobenzene (NB) in solid, solution and vapor state with high sensitivity and selectivity. Sensor IPA showed noteworthy colorimetric and fluorometric quenching in fluorescence emission when exposed to NB. Small size of NB and involvement of photoinduced electron transfer (PET) lead to detection of NB down to 60 nM. IPA-NB interaction was studied through UV-Vis. spectroscopic studies along with fluorescence spectroscopy. Moreover, 1H and 13C NMR titration experiments provided additional support for determination of interaction type. Furthermore, by using density functional theory (DFT) calculations, thermodynamic stability was studied. Additionally, non-covalent interactions (NCI), frontier molecular orbitals (FMO), density of states (DOS), were investigated for providing further evidence of nitrobenzene sensing and its interaction with sensor. Natural bond orbital (NBO) analysis was carried out for charge transfer studies. Quantum theory of atom in molecule (QTAIM) and SAPT0 studies provided information about interaction points and binding energy. Additionally, IPA was investigated for NB sensing in real water samples, and its effective participation in solid state on-site detection as well as in solution phase was brought to light along with logic gate construction.

Recent Advances in Nanoscale Zero-Valent Iron (nZVI)-Based Advanced Oxidation Processes (AOPs): Applications, Mechanisms, and Future Prospects

The fast rise of organic pollution has posed severe health risks to human beings and toxic issues to ecosystems. Proper disposal toward these organic contaminants is significant to maintain a green and sustainable development. Among various techniques for environmental remediation, advanced oxidation processes (AOPs) can non-selectively oxidize and mineralize organic contaminants into CO2, H2O, and inorganic salts using free radicals that are generated from the activation of oxidants, such as persulfate, H2O2, O2, peracetic acid, periodate, percarbonate, etc., while the activation of oxidants using catalysts via Fenton-type reactions is crucial for the production of reactive oxygen species (ROS), i.e., •OH, •SO4-, •O2-, •O3CCH3, •O2CCH3, •IO3, •CO3-, and 1O2. Nanoscale zero-valent iron (nZVI), with a core of Fe0 that performs a sustained activation effect in AOPs by gradually releasing ferrous ions, has been demonstrated as a cost-effective, high reactivity, easy recovery, easy recycling, and environmentally friendly heterogeneous catalyst of AOPs. The combination of nZVI and AOPs, providing an appropriate way for the complete degradation of organic pollutants via indiscriminate oxidation of ROS, is emerging as an important technique for environmental remediation and has received considerable attention in the last decade. The following review comprises a short survey of the most recent reports in the applications of nZVI participating AOPs, their mechanisms, and future prospects. It contains six sections, an introduction into the theme, applications of persulfate, hydrogen peroxide, oxygen, and other oxidants-based AOPs catalyzed with nZVI, and conclusions about the reported research with perspectives for future developments. Elucidation of the applications and mechanisms of nZVI-based AOPs with various oxidants may not only pave the way to more affordable AOP protocols, but may also promote exploration and fabrication of more effective and sustainable nZVI materials applicable in practical applications.

GO accelerate iron oxides formation and tetrabromobisphenol A removal enhancement in the GO loaded NZVI system

Tetrabromobisphenol A (TBBPA) is an emerging persistent organic pollutant, which is very difficult to remove by common methods. In this study, the GO-load nanoscale zero-valent iron (NZVI/GO) was fabricated and optimized to improve the reaction rate and removal efficiency for TBBPA reliably and efficiently. The results showed that GO-load significantly reduced the self-aggregation of NZVI and the aggregate size decreased by 50.00% (1400-700 nm). Meanwhile, GO significantly improved the reaction rate k_obs (1.11 ± 0.11 h^-1) of TBBPA in the NZVI/GO system compared to the NZVI (0.40 ± 0.08 h^-1) system, and this increment was more pronounced (177.5%) when the mass ratio of NZVI-to-GO reached 1.0 than other mass ratios. Furthermore, X-Ray Diffraction and X-ray photoelectron spectroscopy analysis suggested that the Fe²⁺ transformation was changed and enriched by the GO. Only magnetite (Fe₃O₄) was detected on the surface of NZVI, whereas the maghemite (γ-Fe₂O₃), hematite (α-Fe₂O₃), and Fe₃O₄ were detected on the interface of NZVI/GO, which further performed the complexation adsorption through the -OH of TBBPA. This specific complexation adsorption is another potential accelerated removal mechanism for TBBPA and intermediates within the NZVI/GO system. This research has put forward a new perspective for widening the application of TBBPA removal using the synergistic effect between GO and NZVI.

Synchronous N and P Removal in Carbon-Coated Nanoscale Zerovalent Iron Autotrophic Denitrification─The Synergy of the Carbon Shell and P Removal

Fe⁰ is a promising electron donor for autotrophic denitrification in the simultaneous removal of nitrate and phosphorus in low C/N wastewater. However, P removal may inevitably inhibit bio-denitrification. It has not been well recognized and led to an overdose of iron materials. This study employed carbon-coated zerovalent iron (Fe⁰@C) to support autotrophic denitrification to mitigate the inhibition effects of P removal and enhance both N and P removal. The critical role of the carbon shell in Fe⁰@C was to block the direct contact between Fe⁰ and P and NO₃^--N, to maintain the Fe⁰ activity. Besides, P inhibited the chemical reduction of NO₃^--N by competing for Fe⁰ active sites. This indirectly boosted H₂ generation and promoted bio-denitrification. P removal displayed negligible effects on microbial species but indirectly enhanced the nitrogen metabolic activities because of promoted H₂ in Fe⁰@C-based autotrophic denitrification. Bio-denitrification, in turn, strengthened Fe-P co-precipitation by promoting the formation of ferric hydroxide as a secondary adsorbent for P removal. This study demonstrated an efficient method for simultaneous N and P removal in autotrophic denitrification and revealed the synergistic interactions among N and P removal processes.

Hydrothermally assisted synthesis of nano zero-valent iron encapsulated in biomass-derived carbon for peroxymonosulfate activation: The performance and mechanisms for efficient degradation of monochlorobenzene

A facile, green and easily-scalable method of synthesizing stable and effective nano zero-valent iron (nZVI)‑carbon composites for peroxymonosulfate (PMS) activation was highly desirable for in-situ groundwater remediation. This study developed a two-step hydrothermally assisted carbothermal reduction method to prepare nZVI-encapsulated carbon composite (Fe@C) using rice straw and ferric nitrate as precursors. The hydrothermal reactions were conducive to iron loading, and carbothermal temperature was crucial for the aromatization and graphitization of hydrothermal carbonaceous products, the reductive transformation of iron oxides into nZVI and the development of porous structure in composites. At carbothermal temperature of 800 °C following hydrothermal reactions, the stable Fe@C800 with nZVI encapsulated in the spherical carbon shell was obtained and exhibited the best catalytic performance for PMS activation and the degradation of monochlorobenzene (MCB) in a wide range of pH values (3-11) with removal efficiency after 120 min reaction and first-order kinetic rate constant (k₁) of 98.7% and 0.087 min^-1 respectively under the optimum conditions of 10 mM PMS and 0.2 g·L^-1 Fe@C800. The inhibiting effects of common co-existed anions (i.e., Cl^-, HCO₃^- and H₂PO₄^-) and humic acid in groundwater on the removal of MCB in Fe@C800/PMS system was also investigated. Both OH-dominated radical processes and nonradical pathways involving ¹O₂ and surface electron transfers were accounted for PMS activation and MCB removal. The inner nZVI was protected by the carbon shell, endowing Fe@C800 with high reactivity and good reusability. Additionally, 81.2% and 73.5% of MCB removal rates were achieved in tap water and actual contaminated groundwater respectively. This study not only provided a novel strategy to synthesize highly effective and stable nZVI‑carbon composites using the agricultural biomass waste for PMS induced oxidation of organic contaminants in groundwater, but also enhanced the understanding on the activation mechanism of iron‑carbon based catalysts towards PMS.

Aminopolycarboxylic acids modified oxygen reduction by zero valent iron: Proton-coupled electron transfer, role of iron ion and reactive oxidant generation

The oxygen reduction reaction (ORR) activated by Fe⁰ in the presence of three aminopolycarboxylic acids (CAs), i.e. nitrilotriacetic acid (NTA), ethylenediamine-N,N'-disuccinic acid (EDDS) and ethylenediaminetetraacetic acid (EDTA), for the degradation of sulfamethazine (SMT) was investigated. At optimum conditions, Fe⁰/EDDS/O₂, Fe⁰/EDTA/O₂ and Fe⁰/NTA/O₂ systems presented SMT removal of 58.2%, 75.3% and 93.8%, respectively, being much higher than that in the Fe⁰/O₂ system (1.36%). The generation of surface-bound Fe²⁺ (Fe²⁺) and dissolved iron ion was enhanced by CAs. ORR through a two-electron transfer pathway was mainly responsible for H₂O₂ generation in NTA and EDTA systems, while a single-electron ORR was the major source for producing H₂O₂ in EDDS system. •OH produced by the homogeneous reaction of Fe²⁺ and H₂O₂ was the main species for SMT degradation. Fe⁰/EDDS/O₂ produced more ¹O₂ than Fe⁰/EDTA/O₂ and Fe⁰/NTA/O₂; however, the radical contributed negligibly to SMT removal. The caging effect of CAs might be a major factor influencing the reaction rate of Fe²⁺ and O₂. CAs provided protons to accelerate the electron transfer, the production of Fe²⁺ and thus the contaminant removal. This study is of great significance for revealing ORR mechanisms in the Fe⁰-chelate system.

New insights into iron/nickel-carbon ternary micro-electrolysis toward 4-nitrochlorobenzene removal: Enhancing reduction and unveiling removal mechanisms

The ternary micro-electrolysis material iron/nickel-carbon (Fe/Ni-AC) with enhanced reducibility was constructed by introducing the trace transition metal Ni based on the iron/carbon (Fe/AC) system and used for the removal of 4-nitrochlorobenzene (4-NCB) in solution. The composition and structures of the Fe/Ni-AC were analyzed by various characterizations to estimate its feasibility as reductants for pollutants. The removal efficiency of 4-NCB by Fe/Ni-AC was considerably greater than that of Fe/AC and iron/nickel (Fe/Ni) binary systems. This was mainly due to the enhanced reducibility of 4-NCB by the synergism between anode and double-cathode in the ternary micro-electrolysis system (MES). In the Fe/Ni-AC ternary MES, zero-iron (Fe⁰) served as anode involved in the formation of galvanic couples with activated carbon (AC) and zero-nickel (Ni⁰), respectively, where AC and Ni⁰ functioned as double-cathode, thereby promoting the electron transfer and the corrosion of Fe⁰. The cathodic and catalytic effects of Ni⁰ that existed simultaneously could not only facilitate the corrosion of Fe⁰ but also catalyze H₂ to form active hydrogen (H*), which was responsible for 4-NCB transformation. Besides, AC acted as a supporter which could offer the reaction interface for in-situ reduction, and at the same time provide interconnection space for electrons and H₂ to transfer from Fe⁰ to the surface of Ni⁰. The results suggest that a double-cathode of Ni⁰ and AC could drive much more electrons, Fe²⁺ and H*, thus serving as effective reductants for 4-NCB reduction.