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[Display omitted] • An energy band-matched efficient photo-Fenton-like reactor was constructed. • Graphitic carbon ring induced successive built-in electric field for PMS activation. • CoWO 4 /GD-CN universally degraded representative contaminants in different fields. • The reaction mechanism enhanced by gradient graphitic carbon rings was proposed. The heterojunction with matched energy band enables efficient peroxymonosulfate (PMS)-based photo-Fenton-like reaction. Nevertheless, the rapid photogenerated charge separation and transfer has been challenging. Herein, we precisely constructed an efficient heterogeneous photo-Fenton-like reactor with successive built-in electric field by gradient doping of coplanar graphitic carbon rings (C gra) into cobalt tungstate/graphitic carbon nitride (CoWO 4 /GD-CN) heterostructure. The as-prepared CoWO 4 /GD-CN exhibited remarkable enhancement with a tetracycline hydrochloride degradation rate constant (0.776 min−1) higher than that of CoWO 4 /CN (0.507 min−1). Theoretical and experimental results demonstrated that the successive built-in electric field enhanced by gradient-doped coplanar C gra ring accelerated photogenerated electrons transfer from the innermost to the outmost layer of CoWO 4 /GD-CN. This transfer drove Co(III)/Co(II) conversion for accelerated PMS activation, leading to enhanced degradation reactivity. CoWO 4 /GD-CN had excellent degradability towards representative contaminants, including carbamazepine (1.0 min−1), 4-chlorophenol (0.920 min−1), sulfamethoxazole (0.90 min−1), bisphenol A (0.933 min−1), atrazine (0.829 min−1), ciprofloxacin (0.589 min−1) and norfloxacin (0.617 min−1) in CoWO 4 /GD-CN/PMS/vis system, respectively. This work provided a novel insight into the gradient-dope modulated photo-Fenton-like reaction and guided the design of efficient photo-Fenton-like reactor. [ABSTRACT FROM AUTHOR]

[Display omitted] • CoWO 4 /g-C 3 N 4 with matched energy band structure was successfully synthesized. • Hindrance of interfacial barrier in conventional heterojunctions was much reduced. • Pollutants degradation efficiency was greatly improved compared to previous work. • O 2 −, 1O 2 and SO 4 − played an important role in the degradation process of TCH. • The degradation mechanism and pathways of TCH were proposed. Activation of peroxymonosulfate (PMS) by constructing heterojunctions using cobalt-based catalysts under visible light has been widely used for the treatment of emerging pollutants. However, the high recombination rate of photogenerated charge carrier severely inhibited the degradation efficiency of photocatalysts. Herein, CoWO 4 /g-C 3 N 4 was prepared as an efficient PMS activator for the degradation of typical antibiotics according to a rational structural and compositional design via the matching principle of Fermi levels. The morphology, structure and chemical composition of the composites were investigated through a series of characterizations. The tetracycline hydrochloride (TCH) degradation efficiency of 2CoWO 4 /g-C 3 N 4 reached 99.9 % in 10 min at PMS/vis system, with the mineralization performance at 59.8 %. The excellent degradation performance was attributed to the unimpeded photogenerated carrier separation and transfer caused by the matched energy band structure between CoWO 4 and g-C 3 N 4. Also, its degradation performance for Ciprofloxacin (CIP) and Norfloxacin (NOF) was better than the reported non-Fermi level matched heterojunction composed of CoWO 4 and g-C 3 N 4. The results of quenching experiments verified the production and consumption processes of reactive oxidants O 2 −, 1O 2 , SO 4 − and OH. The degradation pathways and mechanism of TCH were also extrapolated in detail. This research provided an in-depth theoretical basis for the design and construction of highly efficient photocatalysts. [ABSTRACT FROM AUTHOR]

Abstract: A visible-light responsive anatase TiO2 was synthesized with a facile peptization-reflux method at 120°C, using tetrabutyl titanate (TBT) as the titanium precursor. According to the results of various experiments and characterizations, we observed that in the low-temperature synthetic process of TiO2 catalysts, there is an equilibrium of hydrolytic decomposition and re-combination of Ti–(O–R) bond from the titanium precursor; the presence of acid and hydrolysis products (n-butanol) cooperatively lead to the retention of more alkoxyl groups on the anatase surface. Upon visible light irradiation, excited electrons could be generated from these alkoxyl-derived surface states, and the photocatalytic reactions through a ligand-to-metal charge transfer (LMCT) process were thus initiated. [ABSTRACT FROM AUTHOR]

Limited peroxymonosulfate (PMS, HSO 4 −) activation efficiency resulted from slow metal reduction has been a challenge in visible-light (vis) assisted sulfate radical-based oxidation. Herein, a Z-scheme photocatalyst composed of nitrogen-defect-rich graphitic carbon nitride nanosheets embedded with nickel cobaltate nanoparticles (NiCo 2 O 4 /g-C 3 N 4 -N vac) was elaborately designed to accelerate Ni(III)/Ni(II) and Co(III)/Co(II) cycles for PMS activation in PMS/vis system. The NiCo 2 O 4 /g-C 3 N 4 -N vac exhibited remarkable enhancement with a tetracycline hydrochloride (TCH) degradation rate constant (0.1168 min−1), higher than those of NiCo 2 O 4 /g-C 3 N 4 (0.0724 min−1) and g-C 3 N 4 (0.0233 min−1), respectively. Also, the removal efficiencies of 95.5%, 94.2%, 98.0% and 91.4% for carbamazepine, 4-chlorophenol, atrazine and p-nitrophenol were achieved within 30 min, respectively. Theoretical and experimental results suggested that nitrogen (N) vacancies modulated electric structure to build Z-scheme-charge-transfer platform for rapid reduction of Ni(III) and Co(III), thereby accelerating PMS activation for remarkable removal of emerging pollutants. NiCo 2 O 4 /g-C 3 N 4 -N vac exhibited excellent stability and corresponding electrical energy per order (EE/O) in different water matrix was evaluated. Additionally, TCH degradation behavior, pathways and toxicity of products were analyzed, respectively. This work provided an novel paradigm to design the efficient photo-activator of PMS for environmental remediation. [Display omitted] • Z-scheme NiCo 2 O 4 /g-C 3 N 4 -N vac was designed to accelerate PMS activation. • N vacancies lower barrier for achieving Z-scheme charge transfer route. • NiCo 2 O 4 /g-C 3 N 4 -N vac had remarkable performance for various emerging pollutants. • Lower EE/O values in different water matrix engendered more economic benefits. • Degradation pathway and toxicity of products was proposed. [ABSTRACT FROM AUTHOR]

Z-scheme photocatalytic system was considered as a promising strategy to tackle environmental pollution crises. However, photogenerated charges behaviors of Z-scheme photocatalyst were still ambiguous, particularly for charge-recombination process occurring at the interface of Z-scheme heterojunctions. In this work, a solid-state heterojunction photocatalyst consisting of BiOI and g-C 3 N 4 was fabricated to reveal the Z-scheme transfer process of photogenerated charge. The morphology, physical and optical properties were characterized in detail. The as-prepared BiOI/g-C 3 N 4 composites exhibited higher reduction efficiency of Cr(VI) than that of pure BiOI and g-C 3 N 4 , and 79.2% of Cr(VI) removal was achieved after 15 min visible light irradiation (λ > 420 nm). The remarkable degradation performance was due to efficient separation and transfer of photogenerated charge in a direct Z-scheme path. More importantly, the non-radiative recombination process of photoinduced carriers occurring at the interface between BiOI and g-C 3 N 4 was confirmed by the photoluminescence (PL), photoacoustics (PA) spectroscopy, work function (WF) and electron spin-resonance spectroscopy (ESR) measurement. This work shows that appropriate increasing the non-radiative recombination center may help to improve the charge recombination occurring at the interface so as to enhance photocatalytic degradation activity of Z-scheme photocatalytic system. Image 1 • The way of charge-recombination at the interface of BiOI/g-C 3 N 4 was investigated. • Remarkable photoreduction performance of Cr(VI) with BiOI/g-C 3 N 4 was demonstrated. • A new mechanism understanding for high-performance was proposed. [ABSTRACT FROM AUTHOR]

Heterogeneous photo-Fenton technology has drawn tremendous attention for removal of recalcitrant pollutants. Fe-based metal-organic frameworks (Fe-MOFs) are regarded to be superior candidates in wastewater treatment technology. However, the central metal sites of the MOFs are coordinated with the linkers, which reduces active site exposure and decelerates H 2 O 2 activation. In this study, a series of 2, 5-dioxido-1, 4-benzenedicarboxylate (H 2 DOBDC)-functionalized MIL-100(Fe) with enhanced degradation performance was successfully constructed via solvothermal strategy. The modified MIL-100(Fe) displayed an improvement in photo-Fenton behaviors. The photocatalytic rate constant of optimized MIL-100(Fe)-1/2/3 are 2.3, 3.6 and 4.4 times higher compared with the original MIL-100(Fe). The introduced H 2 DOBDC accelerates the separation and transfer in photo-induced charges and promotes Fe(II)/Fe(III) cycle, thus improving the performance. •OH and •O 2 − are main reactive radicals in tetracycline (TCH) degradation. Dealkylation, hydroxylation, dehydration and dealdehyding are the main pathways for TCH degradation. [ABSTRACT FROM AUTHOR]

• Four different electron-donating capacity groups in COFs were compared. • Stronger electron-donating capacity is beneficial for greater conjugation effects. • Electron-donating groups are more favorable for electron push-pull effects. • MeO-COF achieved superior activity for photocatalytic H 2 O 2 evolution under air. Electron-donating group modification on covalent organic frameworks (COFs) would reasonably stimulate photocatalytic activity. However, the structure-activity relationship between the electron-donating capacity and the photocatalytic activity of electron-donating functional COFs remains greatly obscure. Herein, a series of functionalized hydrazone-linked COFs containing different electron-donating capacity groups (R-COF, R = H, Me, MeO, OH) were constructed. The results suggest that the existence of substituents with strong electron-donating capacity in R-COFs can enhance the conjugation effect and thereby accelerate the separation and transfer of photogenerated electron-hole pairs. And the stronger electron-donating capacity of groups are more favorable for the electron push-pull effect, which is beneficial for photocatalytic H 2 O 2 production. Among them, MeO-COF had the highest H 2 O 2 generation performance without sacrificial agents under air (847.9 μmol g−1 h−1), which is 4.95 times higher than that of H-COF. This work provides insights for the design of functionalized COFs to achieve efficient photocatalytic H 2 O 2 production. In this work, four hydrazone-linked COFs with different electron-donating groups are constructed to revealed the relationship between the electron-donating capacity of the groups and the photocatalytic H 2 O 2 performance. Electron-donating groups were introduced to the backbone of the COFs through the alteration of the aldehyde node, which produced a strong conjugation effect and accelerated the separation and transfer of charge carriers. And the electron push-pull effect is enhanced with the increase of the electron donating capacity of the groups, which is beneficial for photocatalytic H 2 O 2 evolution. In summary, MeO-COF exhibits the best photocatalytic H 2 O 2 evolution because of the strong electron-donating capacity of methoxy in its backbone. [Display omitted] [ABSTRACT FROM AUTHOR]

Citric acid modified MIL-88A(Fe) is beneficial for active site exposure, visible light absorption, charge carrier transfer and Fe2+/Fe3+ redox cycle, thus achieving an enhanced photo-Fenton performance. [Display omitted] • Controllable CA substitution results in homogeneous MIL-88A(Fe) modification. • CA-modified MIL-88A(Fe) exhibits enhanced photo-Fenton activity for MB and CBZ degradation. • Ligand substitution is beneficial for charge carrier transfer and Fe2+/Fe3+ redox cycle. Fe-based metal organic framework with high active site exposure, wide light absorption and fast H 2 O 2 activation are pivotal for photo-Fenton degradation of contaminants. However, insufficient active site exposure, weak visible light adsorption and low charge transfer efficiency in iron-oxo clusters usually lead to the slow Fe(II)/Fe(III) cycle. In this study, we develop a novel citric acid (CA)-modified MIL-88A(Fe) strategy to boost photo-Fenton efficiency by accelerating Fe(II)/Fe(III) cycle for emerging contaminants removal. Relationship between CA coordination mode and photo-Fenton performance was studied by using methylene blue (MB) and carbamazepine (CBZ) as model contaminants. It was found that the degradation rate constants of MIL-88A(Fe)-CA-3 were 6.5 and 2.6 times higher than those in the pristine MIL-88A(Fe) for MB and CBZ degradation, respectively. The optimized MIL-88A(Fe)-CA-3 also exhibited good recyclability, enabling multiple cycles in photo-Fenton reaction. The results of experimental characterizations and density functional theory calculations demonstrated that ligand substitution was conductive to active site exposure, visible light absorption, charge carrier transfer and Fe2+/Fe3+ redox cycle, which are responsible for an improved photo-Fenton performance. [ABSTRACT FROM AUTHOR]