Solar radiation is a sustainable, unlimited source of energy for electricity and chemical reactions, yet the conversion efficiency of actual processes is limited and controlled by photocarriers ...migration and separation. Enhancing the conversion efficiency would require to suppress the recombination of photogenerated electron–hole pairs and improve the low redox potentials. This can be done during the growth of step-scheme (S-scheme) heterojunctions. Here we review the charge transfer of S-scheme heterojunctions involving a reduction and oxidation photocatalyst in staggered band arrangement with Fermi level differences. We present factors determining the validation of the S-scheme mechanism with respective characterization techniques, including in situ and ex situ experiments, and theoretical studies. We show mechanistic drawbacks of traditional photocatalytic systems to highlight the advantages of S-scheme photocatalysts. We describe co-catalyst loading, bandgap tuning, and interfacial optimization that ultimately achieve highly efficient photocatalysis. Last, application for water splitting, CO
2
conversion, pollutant degradation, bacterial inactivation and others is discussed.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
As an alluring metal-free polymeric semiconductor material, graphite-like carbon nitride (g-C
3
N
4
; abbreviated as GCN) has triggered a new impetus in the field of photocatalysis, mainly favoured ...from its fascinating physicochemical and photoelectronic structural features. However, certain inherent drawbacks, involving rapid reassembly of photocarriers, low specific surface area and insufficient optical absorption, limit the wide-range applicability of GCN. Generation of 0D point defects mainly by introducing vacancies (C and/or N) into the framework of GCN has spurred extensive consideration owing to their distinctive qualities to manoeuvre substantially, the optical absorption, radiative carrier isolation, and surface photoreactions. The present review endeavours to summarise a comprehensive study on vacancy defect engineered GCN. Starting from the basic introduction of defects and C/N vacancy modulated GCN, numerous advanced strategies for the controlled designing of vacancy rich GCN have been explored and discussed. Afterwards, light was thrown on the various substantial technologies which are useful for characterising and identifying the introduction of defects in GCN. The salient significance of defect engineering in GCN has been reviewed concerning its impact on optical absorption, charge isolation and surface photoreaction ability. Typically, the achievement of defect engineered GCN has been scrutinised toward various applications like photocatalytic water splitting, CO
2
conversion, N
2
fixation, pollutant degradation, and H
2
O
2
production. Finally, the review ends with conclusions and vouchsafing future challenges and opportunities on the intriguing and emerging area of vacancy defect engineered GCN photocatalysts.
As an alluring metal-free polymeric semiconductor material, graphite-like carbon nitride (g-C
3
N
4
; abbreviated as GCN) has triggered a new impetus in the field of photocatalysis, mainly favoured from its fascinating physicochemical and photoelectronic structural features.
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Recently, layered bismuth oxyhalides (BiOX, X=F, Cl, Br and I) have received significant attention as potential photocatalysts for energy and environment applications. However, ...limited visible light activity and recombination of photogenerated charge carriers limit their applications for photocatalytic water purification. In this review, various strategies such as heterojunction formation, metal/non-metal doping, interface modification, enhancement in Bi content, inner coupling between different BiOX photocatalyst, use of sensitizers and creation of oxygen vacancies was deliberated for improved photocatalytic performance of BiOX. The integration of BiOX with other photocatalysts, mechanism for enhanced activity and conclusive outlook with future challenges was also elaborated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Graphitic carbon nitride (GCN) was coupled with NiFe2O4.•GCN/NiFe2O4 was effectively used to mineralize oxytetracycline antibiotic.•Photocatalysis was substantially affected by ...adsorption process.•GCN/NiFe2O4 was magnetically separated in 2 min from reaction solution.•GCN/NiFe2O4 has significant stability for ten catalytic cycles.
In this work, we report the applicability of NiFe2O4 loaded graphitic carbon nitride (GCN/NiFe2O4) as a magnetic photocatalyst for wastewater treatment. Herein, GCN was prepared by thermal condensation of urea and successfully loaded with NiFe2O4 nanoparticles. GCN/NiFe2O4 was characterized by FESEM, HRTEM, IR, XRD, VSM and UV visible spectral analysis. High surface area of GCN/NiFe2O4 was suitable for adsorption coupled photocatalysis. The GCN/NiFe2O4 exhibited significant photocatalytic activity for mineralization of oxytetracycline (OTC) antibiotic under solar light. The OTC was completely mineralized in 8 h during simultaneous adsorption and photocatalysis process. The rate of OTC degradation was optimal at pH 5. GCN/NiFe2O4 possessed ferromagnetic behavior and could be easily separated by external magnetic field from waste water. The excellent activity of GCN/NiFe2O4 was due to efficient separation of photogenertaed electron and hole pair. GCN/NiFe2O4 exhibited significant recycle efficiency for ten catalytic cycles.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Semiconductor photocatalyst mediated advanced oxidation processes are regarded as one of the most efficient technologies to mitigate organic pollutants in water. However, poor activity under visible ...light and the recombination of photogenerated electron and hole pairs hinder large scale applicability of semiconductor photocatalysts for water purification. The modification of semiconductor photocatalysts with carbon quantum dots (CQDs) is of high importance due to low toxicity, aqueous stability, enhanced surface area, economic feasibility, good biocompatibility and chemical inertness of CQDs. In this review, we highlight strategies to improve the activity of conventional semiconductor photocatalysts via coupling with CQDs. The enhanced photocatalytic activity of CQD modified narrow and wide band gap photocatalysts is due mainly to up-conversion photoluminescence (UPCL) and the electron reservoir properties of CQDs, while in the case of Z-scheme photocatalysts CQDs act as an electron mediator. Finally, a conclusive outlook and suggested research directions are provided to address challenges such as the inadequate separation of photoinduced charge carriers.
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•Overview of recent development in Carbon Quantum dots (CQDs) based photocatalysis.•Integration of CQDs with other photocatalysts for enhanced photocatalysis.•Elaboration of CQD’s role in enhanced photocatalytic water purification.•Future scope of CQDs based photocatalyst in wastewater treatment.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Heterogeneous photocatalysis employing advanced oxidation has received significant attention for water purification and disinfection. Recently, the excellent photocatalytic and antibacterial ...properties of graphene-based nanomaterials have encouraged the scientists to fabricate better graphene-based nanocomposites with enhanced photoefficiency for degradation of pollutants and disinfection of water resources. This review presents an overview of the various works done on the utilization of graphene-based photocatalytic systems in water purification and, especially, focuses on the strength of graphene-based composite materials in water disinfection. Therefore, after throwing some light on the advanced oxidation processes and basic principles of heterogeneous photocatalysis, the properties of graphene and its derivatives for being employed as photocatalysts and various strategies adopted for improving their photocatalytic activity was discussed thoroughly. Also, the efficiency of graphene-based composites as disinfectants discussed in the preceding section. At the end, a conclusion was drawn to discuss the remaining challenges and prospects for using graphene-based nanocomposites in environmental sciences.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Photocatalytic materials for photocatalysis is recently proposed as a promising strategy to address environmental remediation. Metal-free graphitic carbon nitride (g-C3N4), is an emerging ...photocatalyst in sulfate radical based advanced oxidation processes. The solar-driven electronic excitations in g-C3N4 are capable of peroxo (O‒O) bond dissociation in peroxymonosulfate/peroxydisulfate (PMS/PDS) and oxidants to generate reactive free radicals, namely SO4•− and OH• in addition to O2•− radical. The synergistic mechanism of g-C3N4 mediated PMS/PDS photocatalytic activation, could ensure the generation of OH• radicals to overcome the low reductive potential of g-C3N4 and fastens the degradation reaction rate. This article reviews recent work on heterojunction formation (type-II heterojunction and direct Z-scheme) to achieve the bandgap for extended visible light absorption and improved charge carrier separation for efficient photocatalytic efficiency. Focus is placed on the fundamental mechanistic routes followed for PMS/PDS photocatalytic activation over g-C3N4-based photocatalysts. A particular emphasis is given to the factors influencing the PMS/PDS photocatalytic activation mechanism and the contribution of SO4•− and OH• radicals that are not thoroughly investigated and require further studies. Concluding perspectives on the challenges and opportunities to design highly efficient persulfate-activated g-C3N4 based photocatalysts toward environmental remediation are also intensively highlighted.
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•Advantages of peroxymonosulfate/peroxydisulfate (PMS/PDS) photocatalytic activation are mentioned.•The synergistic heterojunction effect on PMS/PDS over g-C3N4-based photocatalysts is evaluated.•The role of sulfate (SO4•−) radicals for pollutant degradation application are elaborated.•Challenges and future prospects of the photocatalytic activation PMS/PDS are proposed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Global energy demand and pollution are calling for advanced materials such as visible light semiconductor photocatalysts. In particular, cadmium sulfide (CdS) appears promising due to its tunable ...bandgap, high absorption of visible light and excellent optical properties. Here we review the photocatalytic mechanism, properties, synthesis and application to wastewater treatment of CdS photocatalysts. Strategies to improve photocatalytic performance include heteroatom doping, heterojunction formation, morphology and crystallinity modification, hybridization with co-catalysts and the use of carbon materials.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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•Green synthesis of heterojunction via hydrothermal method using bamboo leaves.•Extended visible light absorption and high charge carrier separation.•Enhanced photocatalytic ...degradation efficiency for 2,4 dinitrophenol pollutant.•The improved activity and photostability due to Z-scheme photocatalytic system.
The unique attributes of CQDs, such as low cost, facile synthesis, tremendous photochemical, and physicochemical stability, render them as versatile nanocomposites, as compared to conventional semiconductors. Herein, a green synthesis approach was opted using naturally occurring bamboo leaves as precursors for CQDs production via a facile and efficient hydrothermal method. The fabricated CQDs were exploited for construction of Z-scheme P-doped g-C3N4/AgI/ZnO/CQDs (PGCN) heterojunction by immobilizing AgI/ZnO/CQD on graphitic carbon nitride (g-C3N4), that acts as support targeted for 2, 4-dinitrophenol (DNP) eradication from simulated wastewater. TEM image depicts the presence of different fringes on an agglomerated structure which confirms the formation of nanocrystalline heterostructure. XRD, XPS, FT-IR, and EDX were used to provide structural, morphological information of synthesized samples relating the existence of heterostructure between AgI and ZnO/CQDs with the sheet-like structured g-C3N4 which have undergone successful inclusion of P dopant into g-C3N4 framework. Congruously, the optical properties of modified photocatalyst with suppression in photogenerated electron-hole pair recombination g-C3N4/AgI/ZnO/CQD nanostructure were evidenced by photoluminescence (PL) spectra and UV–Vis diffused reflection spectra (UV–Vis DRS). Synergistic process of adsorption and photocatalysis was effectual for complete mineralization of DNP into CO2, H2O, and inorganic ions. The integration of g-C3N4 to AgI/ZnO with CQDs accelerated photocatalytic activity attributed to electron sink behavior of CQDs. The fabricated Z-scheme P-doped g-C3N4/AgI/ZnO/CQDs photocatalyst exhibited remarkable stability and recyclability for ten consecutive catalytic cycles.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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Graphitic carbon nitride (g-C3N4) as a fascinating visible light active semiconductor photocatalyst has medium band gap, non-toxic nature, stable chemical structure and high thermal ...stability. Recently, intensive researches are focused on photocatalytic activity of g-C3N4 for wastewater treatment. This review demonstrates latest progress in fabrication of graphitic carbon nitride C3N4 incorporated nanocomposite to explore photocatalytic ability for water purification. The g-C3N4-based nanocomposites were categorized as g-C3N4 metal-free nanocomposite, noble metals/g-C3N4 heterojunction, non-metal doped g-C3N4, transition and post transition metal based g-C3N4 nanocomposite. Apart from fabrication methods, we emphasized on elaborating the mechanism of activity enhancement during photocatalytic process.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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