Single atom catalysts (SACs) with the maximized metal atom efficiency have sparked great attention. However, it is challenging to obtain SACs with high metal loading, high catalytic activity, and ...good stability. Herein, we demonstrate a new strategy to develop a highly active and stable Ag single atom in carbon nitride (Ag‐N2C2/CN) catalyst with a unique coordination. The Ag atomic dispersion and Ag‐N2C2 configuration have been identified by aberration‐correction high‐angle‐annular‐dark‐field scanning transmission electron microscopy (AC‐HAADF‐STEM) and extended X‐ray absorption. Experiments and DFT calculations further verify that Ag‐N2C2 can reduce the H2 evolution barrier, expand the light absorption range, and improve the charge transfer of CN. As a result, the Ag‐N2C2/CN catalyst exhibits much better H2 evolution activity than the N‐coordinated Ag single atom in CN (Ag‐N4/CN), and is even superior to the Pt nanoparticle‐loaded CN (PtNP/CN). This work provides a new idea for the design and synthesis of SACs with novel configurations and excellent catalytic activity and durability.
A new Ag single atom in carbon nitride (Ag‐N2C2/CN) photocatalyst with Ag‐N2C2 configuration is developed. It affords fast charge transfer, high Ag loading, and good stability. Noteworthily, the Ag‐N2C2/CN exhibits much better hydrogen evolution activity than Ag‐N4/CN, and even superior to the platinum‐loaded CN.
Indirect electrochemical oxidation by hydroxyl radicals is the predominant degradation mechanism in electrolysis with a boron-doped diamond (BDD) anode. However, this electrochemical method exhibits ...low reactivity in removal of hydrophilic aromatic pollutants owing to mass transfer limitation. In this study, the combination of ultraviolet light and BDD electrolysis could increase the degradation rate of hydrophilic aromatic pollutants by approximately 8–10 times relative to electrolysis alone. According to the results of the scavenging experiments and identification of benzoic acid oxidation products, surface-bound hydroxyl radical (•OH(surface)) was the primary reactive species degrading aromatic pollutants in the BDD electrolysis process, whereas freely-diffusing homogeneous hydroxyl radical (•OH(free)) was the major reactive species in the UV-assisted BDD electrolysis process. Cyclic voltammetry revealed that UV light decomposed H2O2 formed on the BDD anode surface, thus retarding O2 evolution and facilitating •OH(free) generation. This work also explored the potential application of UV-assisted BDD electrolysis in removing COD from bio-pretreated landfill leachate containing high concentrations of hydrophilic aromatic pollutants. This study shed light on the importance of the existing state of •OH on removal of pollutants during BDD electrolysis, and provided a facile and efficient UV-assisted strategy for promoting degradation of hydrophilic aromatic pollutants.
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••OH(surface) is the primary reactive species in BDD electrolysis process.•Hydrophobic organics are easier to be degraded with BDD electrolysis than hydrophilic ones.•UV shifts .•OH(surface) to •OH(free) in UV-assisted BDD electrolysis.•Degradation of hydrophilic organics is dramatically enhanced in UV-assisted BDD electrolysis.•Bio-pretreated landfill leachate is amenable to UV-assisted BDD electrolysis.
•The traditional mineralization path of CN− was overturned in a novel Electro-Fenton system.•CN− could be converted into NO3− but not CNO− by the synergy of •OH and •O2−.•The Electro-Fenton system ...shows the feasibility of practical application for the actual cyanide residue eluent.
Traditional methods of cyanides’ (CN−) mineralization cannot overcome the contradiction between the high alkalinity required for the inhibition of hydrogen cyanide evolution and the low alkalinity required for the efficient hydrolysis of cyanate (CNO−) intermediates. Thus, in this study, a novel Electro-Fenton system was constructed, in which the free cyanides released from ferricyanide photolysis can be efficiently mineralized by the synergy of •OH and •O2−. The complex bonds in ferricyanide (100 mL, 0.25 mM) were completely broken within 80 min under ultraviolet radiation, releasing free cyanides. Subsequently, in combination with the heterogeneous Electro-Fenton process, •OH and •O2− were simultaneously generated and 92.9% of free cyanides were transformed into NO3- within 120 min. No low-toxic CNO− intermediates were accumulated during the Electro-Fenton process. A new conversion mechanism was proposed that CN− was activated into electron-deficient cyanide radical (•CN) by •OH, and then the •CN intermediates reacted with •O2− via nucleophilic addition to quickly form NO3-, preventing the formation of CNO− and promoting the mineralization of cyanide. Furthermore, this new strategy was used to treat the actual cyanide residue eluent, achieving rapid recovery of irons and efficient mineralization of cyanides. In conclusion, this study proposes a new approach for the mineralization treatment of cyanide-containing wastewater.
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Highly porous, three-dimensional (3D) nanostructured composite adsorbents of reduced graphene oxides/Mn3O4 (RGO/Mn3O4) were fabricated by a facile method of a combination of reflux condensation and ...solvothermal reactions and systemically characterized. The as-prepared RGO/Mn3O4 possesses a mesoporous 3D structure, in which Mn3O4 nanoparticles are uniformly deposited on the surface of the reduced graphene oxide. The adsorption properties of RGO/Mn3O4 to antimonite (Sb(III)) and antimonate (Sb(V)) were investigated using batch experiments of adsorption isotherms and kinetics. Experimental results show that the RGO/Mn3O4 composite has fast liquid transport and superior adsorption capacity toward antimony (Sb) species in comparison to six recent adsorbents reported in the literature and summarized in a table in this paper. Theoretical maximum adsorption capacities of RGO/Mn3O4 toward Sb(III) and Sb(V) are 151.84 and 105.50 mg/g, respectively, modeled by Langmuir isotherms. The application of RGO/Mn3O4 was demonstrated by using drinking water spiked with Sb (320 μg/L). Fixed-bed column adsorption experiments indicate that the effective breakthrough volumes were 859 and 633 mL bed volumes (BVs) for the Sb(III) and Sb(V), respectively, until the maximum contaminant level of 5 ppb was reached, which is below the maximum limits allowed in drinking water according to the most stringent regulations. The advantages of being nontoxic, highly stable, and resistant to acid and alkali and having high adsorption capacity toward Sb(III) and Sb(V) confirm the great potential application of RGO/Mn3O4 in Sb-spiked water treatment.
Carbon quantum dots/CdS quantum dots/g-C3N4 (CDs/CdS/GCN) photocatalysts have been designed and prepared. Systematic characterization such as XRD, SEM, TEM, UV, and XPS, were done to confirm the ...composite catalysts of CDs/CdS/GCN. The simultaneous photocatalytic production of hydrogen coupled with degradation of organic contaminants (p-chlorophenol, bisphenol A, and tetracycline, called 4-NP, BPA, and TTC, respectively) was efficiently realized over the resultant CDs/CdS/GCN composites. The as-prepared 3%CDs/10%CdS/GCN exhibits high efficiency of photocatalytic hydrogen evolution from water splitting and photodegradation rates of organic pollutants in aqueous solutions of 4-NP, BPA, and TTC under visible-light illumination since the formation of interfaces between CdS quantum dots and GCN nanosheets leads to an efficient charge separation efficiency. Furthermore, as compared to that in a pure water system, the photocatalytic evolution rate of H2 over the 3%CDs/10%CdS/GCN catalyst in the presence of 4-NP solution is decreased, while the H2 evolution rates increase when BPA or TTC solution were used instead of 4-NP solution under visible-light irradiation. Consequently, 4-NP shows higher photodegradation efficiency than do BPA and TTC in the simultaneous photocatalytic oxidation and reduction system. Aiming at making clear the relationship between the photocatalytic H2 production and the photocatalytic pollutants degradation, density functional theory (DFT) calculations, and liquid chromatography mass spectrometry (LC-MS) were used for a systematic investigation. The present work reports a plausible mechanism of photodegradation of different organic contaminants with synchronous photocatalytic H2 evolution from water and the photocatalytic enhancement of the CDs/10%CdS/GCN catalysts.
Fe-CN/NTE improved degradation of 4-NP coupled with simultaneous photocatalytic H2 evolution under visible light irradiation.
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To achieve an efficient photocatalytic for clean energy ...production and environmental remediation, the highly active Fe-doped and terephthalaldehyde-modified carbon nitride (Fe-CN/NTE) isotypic heterojunction photocatalyst is constructed via a simple annealing method for degradation of organic pollutants with simultaneous resource recovery. The Fe-CN/NTE catalyst exhibits a 93% removal rate of p-nitrophenol (4-NP) and a 1.72 mmol/g H2 evolution rate in 2 h simultaneously under visible light irradiation, which are higher than those of pristine CN, Fe-CN, and NTE, respectively. Photoelectrochemical tests show that the excellent photocatalytic performance of Fe-CN/NTE comes from the improved migration, transportation, and separation of photoinduced charge carriers and expanded light-harvesting range. Moreover, hydroxyl radical (OH), electron (e−), and hole (h+) are the main active species and the rational mechanism of 4-NP photodegradation was proposed based on scavenger measurements and liquid chromatography-mass spectrometry (LC–MS), respectively. Isotypic heterojunction Fe-CN/NTE photocatalyst possesses excellent stability in the H2 evolution and 4-NP degradation during five-run cycle tests, posing as a promising candidate in practical works for organic pollution and energy challenges.
In this study, we develop a new composite material of Fe-Cu/D407 composite via using nanoscale zero-valent iron (nZVI) with copper deposited on chelating resin (D407) to remove nitrate from the ...water. The experimental results show that a remarkable nitrate removal and the selectivity of N2 are 99.9% and 89.7%, respectively, under the anaerobic conditions of Cu/Fe molar ratio of 1:2, pH = 3.0. Even without of inert gas and adjusting the initial pH of the solution, the removal rate of nitrate by Fe-Cu/D407 reached to 85% and the selectivity of nitrogen reached to 55%. Meanwhile, the Fe-Cu/D407 maintained preferable removal efficiency of nitrate (100% - 92%) over a wide pH range of 3–11. In addition, the removal rate of the drinking water, lake water and wastewater from the Fe-Cu/D407 is still very high and the reactivity of Fe-Cu/D407 was relatively unaffected by the presence of dissolved ions in the waters tested. Moreover, the synergetic effect of Fe, Cu and D407 in the composite Fe-Cu/D407 were well investigated for the first time according to the analyses of TPR, XPS and EIS. The catalytic mechanism and denitrification routes were also proposed.
Proposed the reaction mechanism and denitrification routes over the Fe-Cu/D407. Display omitted
•Novel catalyst of Fe-Cu/D407 was designed and prepared.•The Fe-Cu/D407 shows excellent removal efficiency of nitrate and selectivity of N2 over a wide pH range.•Synergetic effect of Fe, Cu and D407 in the Fe-Cu/D407 was firstly investigated.•The catalytic mechanism and denitrification routes of nitrate were proposed.
Singlet oxygen (1O2) is an excellent active species for the selective degradation of organic pollutions. However, it is difficult to achieve high efficiency and selectivity for the generation of 1O2. ...In this work, we develop a graphitic carbon nitride supported Fe single‐atoms catalyst (Fe1/CN) containing highly uniform Fe‐N4 active sites with a high Fe loading of 11.2 wt %. The Fe1/CN achieves generation of 100 % 1O2 by activating peroxymonosulfate (PMS), which shows an ultrahigh p‐chlorophenol degradation efficiency. Density functional theory calculations results demonstrate that in contrast to Co and Ni single‐atom sites, the Fe‐N4 sites in Fe1/CN adsorb the terminal O of PMS, which can facilitate the oxidization of PMS to form SO5.−, and thereafter efficiently generate 1O2 with 100 % selectivity. In addition, the Fe1/CN exhibits strong resistance to inorganic ions, natural organic matter, and pH value during the degradation of organic pollutants in the presence of PMS. This work develops a novel catalyst for the 100 % selective production of 1O2 for highly selective and efficient degradation of pollutants.
The carbon nitride supported Fe single‐atom catalyst (Fe1/CN) with a Fe loading of 11.2 wt % was developed to generate 100 % 1O2 by activating peroxymonosulfate (PMS). The adsorption of terminal O and oxidation of PMS by Fe‐N4 sites played the most important roles for 1O2 generation with 100 % selectivity. As a result, the Fe1/CN activated PMS system exhibited strong resistance to various factors during the degradation of organic pollutants.
The selective oxidation capacity of free radicals in advanced oxidation processes (AOPs) is important for the accurate determination of the degradation pathways of organic contaminants when various ...active species coexist in the catalytic system. In this study, diclofenac sodium (DCF) was selected as a model contaminant due to its toxicity and structural characteristics (containing organic moieties with varying electronegativity). A 3D hexagonal star-shaped cobalt oxide electrode was synthesized and used as the electric anode to simultaneously combine with AOPs based on peroxymonosulfate (EAOPs/PMS) to generate two active species (SO4− and OH) and achieve efficient mineralization of DCF. The selectivity property of the free radicals was investigated by comparing DCF transformation pathways in three systems: EAOPs/PMS (containing both SO4− and OH), EAOPs/PMS + TBA (containing only SO4−), and Fe2+/H2O2 (containing only OH). When present simultaneously, SO4− favored attacking the electron-donating moieties (amino groups and aromatic rings), while OH was more disposed to attack the electron-withdrawing moieties (carboxyl groups and chlorine atoms). This study, for the first time, sheds light on the selective oxidation capacity of coexisting SO4− and OH towards organic moieties with differing electronegativity and provides an in-depth analysis of the degradation pathways of an organic contaminant.
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•The selective oxidation of co-existing SO4− and OH was systematically explored for the first time.•The efficient mineralization of DCF could be achieved in the EAOPs/PMS system.•Through comparing the DCF transformation pathways in three systems, the selective oxidation of SO4− and OH was well investigated.•When they were present simultaneously, SO4− favored to attack on the electron-donating moieties, while OH was disposed to attack the electron-drawing moieties.
The development of novel porous materials have attracted significant attention owing to its possible application in several fields. In this study, we designed a novel covalent organic ...framework-metal-organic framework (COF-MOF) material through an in-situ ligand self-assembly method. The in-situ modified ligands not only act as nucleation sites to form Ti-MOF, but also as a channel to rapidly transfer photogenerated electrons without introducing additional chemical bonds. The photocatalytic hydrogen production rate achieved over B-CTF-Ti-MOF(1:1) was 1975 µmol·g−1·h−1 with an apparent quantum efficiency of 4.76%, which is 11.8 times higher than that of the pure CTF-1. In addition, compared with the sample prepared by separating the ligands (CTF-1/Ti-MOF), B-CTF-Ti-MOF shows excellent activity and stability. Finally, a reasonable photocatalytic mechanism was proposed using the results of electrochemical tests and spectral analyses. This study provides a universal method for the construction of highly efficient and stable COF/MOF materials with excellent properties.
Well-designed unique covalent organic framework-metal-organic framework hybrids (B-CTF-Ti-MOF) were constructed by using in-situ functionalized ligands as nucleation sites and electronic transmission channels to boost the photocatalytic performance of the material.
