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
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
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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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•Drawbacks of graphitic carbon nitride photocatalyst were reviewed.•Noble metal free doping was elaborated as effective strategy.•Role of metal and non-metal dopants was ...explored.•Synthesis methods for fabrication of noble metal free doped g-C3N4 were discussed.•Conclusive outlook along with future prospective was provided.
Extensive contamination of water bodies by textile dyeing industries, organic pollutants and agricultural waste has emerged water pollution as one of the major global environmental crisis. The effect of this gross negligence is posing serious threats to human health therefore today; conserving water resources for the essence of life is of grave concern. Recently, advancements in photocatalytic properties of graphitic carbon nitride (g-C3N4) for wastewater treatment have gained tremendous interest in research. However, pristine g-C3N4 suffers from bottlenecks such as low surface area, rapid recombination of photo-generated electron–hole pairs and insufficient light absorption which thereby, reduces the photocatalytic degradation activity. Hitherto, noble metals have been widely utilized as dopants but are cost ineffective, rarely found and are difficult to recover. In this updated and all-inclusive review we have briefly discussed photocatalysis mechanism, primarily focused on non-precious elemental doping via various synthesis techniques of noble metal free doped g-C3N4 photocatalysts. Typically metal, non-metal, rare earth metal doping and co-doping have been explored, which demonstrates the synergistic behavior of the doped nanocomposites in modulation of electronic structure, broaden the visible light absorption range, enhancement in photocatalytic wastewater remediation ability to obtain maximum pollutant eradication. Summary remarks conclude the review with valuable knowledge of noble metal free doped g-C3N4 photocatalysts for water purification and sheds light on current challenges and crucial issues associated with its commercialization. The future aspect aims at designing of efficient solar light driven photocatalysts for application in various domains i.e. production of H2 and O2, reduction of CO2, practical use of solar cells, treatment of wastewater, air purification and environmental conservation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The vaccine innovation is a ubiquitous preventive measure to the transmission of highly infectious SARS-COV-2. The ongoing mass coronavirus vaccination programmes have inadvertently become the bulk ...producers of biomedical and plastic waste triggering severe impact on the environment. The sustainable management of bio hazardous vaccine waste in particular; syringes, needles, used/un-used vials and single-use plastic equipment is of utmost importance. This perspective presents a critical point of view in terms of the generated vaccine waste and the subsequent knock-on effect on all aspects of ecosystem. The discussion includes dire consequences due to the release of huge amount of plastic-based personal protective equipment into marine environment. The pivotal crisis of CO2 emission during the manufacture and storage of different vaccines has contributed to global warming. The unavoidable generation of microfibers upon incineration, autoclaving, pyrolysis and open dumping of vaccine waste has further jeopardized the environment. In this vein, exploration of biodegradable materials for vaccine inoculation and development of green technologies for sound waste management is suggested to mitigate the environment pollution.
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•Surge in vaccine waste is observed during mass vaccination campaigns.•Marine pollution and CO2 gas emission are major global disruptions.•Incineration, autoclaving, chemical disinfection for vaccine waste treatment.•Substitution of vaccine tools by biodegradable polymers are promising
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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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Nowadays, increasing extortions regarding environmental problems and energy scarcity have stuck the development and endurance of human society. The issue of inorganic and organic ...pollutants that exist in water from agricultural, domestic, and industrial activities has directed the development of advanced technologies to address the challenges of water scarcity efficiently. To solve this major issue, various scientists and researchers are looking for novel and effective technologies that can efficiently remove pollutants from wastewater. Nanoscale metal oxide materials have been proposed due to their distinctive size, physical and chemical properties along with promising applications. Cupric Oxide (CuO) is one of the most commonly used benchmark photocatalysts in photodegradation owing to the fact that they are cost-effective, non-toxic, and more efficient in absorption across a significant fraction of solar spectrum. In this review, we have summarized synthetic strategies of CuO fabrication, modification methods with applications for water treatment purposes. Moreover, an elaborative discussion on feasible strategies includes; binary and ternary heterojunction formation, Z-scheme based photocatalytic system, incorporation of rare earth/transition metal ions as dopants, and carbonaceous materials serving as a support system. The mechanistic insight inferring photo-induced charge separation and transfer, the functional reactive radical species involved in a photocatalytic reaction, have been successfully featured and examined. Finally, a conclusive remark regarding current studies and unresolved challenges related to CuO are put forth for future perspectives.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this work, visible light-active sulphur doped graphitic carbon nitride coupled with Ni–Fe layered double hydroxide (SGCN/Ni–Fe LDH) was prepared through co-precipitation procedure using ...commercially available thiourea, nickel nitrate, and ferric nitrate. The surface morphology characterization showed LDH crystallite growth onto the surface of SGCN, exploiting the delocalized π-electrons of graphitic structure to attain chemical stability. The synthesized photocatalyst exhibited 98% 2,4-dinitrophenol (DNP) photodegradation within 120 min of visible light irradiations, which was surprisingly high compared to 60 and 55% obtained for bare GCN and Ni–Fe LDH samples. This photo removal efficiency could be due to suitable bandgap energy, layered graphitic and brucite Ni–Fe layered structures, and sufficient pollutant adherence to active sites provided by incorporation of S dopant into bare GCN. The characterization results obtained by cyclic voltammetry graph photoluminescence and electrochemical impedance spectra indicated minimum charge carrier recombination due to the type-II charge transfer route along with an active generation of ⋅O
2
−
and h
+
as dominant reactive species participating in DNP mineralization into more unaffected inorganic ions. The photocatalytic activity enhanced in an acidic medium at optimized parameters, i.e., pH 4, photocatalyst dosage 50 mg in 50 mL solution, and DNP concentration 1.0 × 10
−4
mol/dm
3
, due to ionic interactions between negatively charged DNP and positive intercalated structure of Ni–Fe LDH. The as-prepared photocatalyst photodegradation ability was retained after 5 catalytic cycles, confirming its environmentally-compatible usage in water treatment.
Solar illumination is a promising source of primary energy to reduce global warming and to clean polluted waters, thus fostering research of the design of efficient photocatalysts for hydrogen ...production by water splitting and for contaminant degradation. In particular, photocatalysis by indium sulfide (In
2
S
3
) is drawing attention due to its suitable narrow bandgap of 2.0–2.3 eV for visible light harnessing, yet large-scale application of unmodified In
2
S
3
is limited. Here we review the photocatalyst criteria for water splitting, the synthesis and morphological manipulations of In
2
S
3
, the synthesis of heterojunctions by coupling semiconductors to increase performance, and doping In
2
S
3
. In
2
S
3
-based heterojunctions, i.e., traditional type II, all-solid-state, and direct
Z
-scheme photocatalytic systems show benefits such as larger charge separation, broad solar spectrum absorption, and amended conduction band and valence band edge potentials for maximum pollutant removal and H
2
production. The effect of dopant incorporation on electronic modulations of In
2
S
3
is explained by the density functional theory.
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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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Considering the current scenario of rising environmental and energy concerns, engineering of Z-scheme photocatalytic systems is in the spotlight. The prime reason for this includes ...efficient redox abilities and effective space separation along with the migration of photoinduced charge carriers over conventional heterojunction systems. Herein we foreground the stumbling blocks of traditional heterojunction systems and enlighten the generations of Z-scheme photocatalysis originating from liquid-phase to direct Z-scheme photocatalytic systems. We provide substantial criteria and selection aspects of choosing reductive type photocatalysts as a potential aspirant for the Z-scheme photocatalytic system. As Z-scheme photocatalytic systems render effective space separation of photogenerated carriers, active species generation, wide optical absorption and amended redox ability. We focus on comprehensive illustration of all solid-state and direct Z-scheme photocatalysts by coupling reductive type photocatalysts with other semiconductor material and explored their potential for efficacious conversion of solar energy into functional energy. Herein, we aim to provide in-depth and updated criteria for selecting Z-scheme photocatalysts for CO2 reduction, water splitting, and nitrogen fixation. Lastly, the article compiles with a conclusive note about future perspectives and challenges accompanying all solid-state and direct Z-scheme Z photocatalysts and their energy conversion applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The prevalence of lethal viral infections necessitates the innovation of novel disinfection techniques for contaminated surfaces, air, and wastewater as significant transmission media of disease. The ...instigated research has led to the development of photocatalysis as an effective renewable solar-driven technology relying on the reactive oxidative species, mainly hydroxyl (OH●) and superoxide (O2●−) radicals, for rupturing the capsid shell of the virus and loss of pathogenicity. Metal-free graphitic carbon nitride (g-C3N4), which possesses a visible light active bandgap structure, low toxicity, and high thermal stability, has recently attracted attention for viral inactivation. In addition, g-C3N4-based photocatalysts have also experienced a renaissance in many domains, including environment, energy conversion, and biomedical applications. Herein, we discuss the three aspects of the antiviral mechanism, intending to highlight the advantages of photocatalysis over traditional viral disinfection techniques. The sole agenda of the review is to summarize the significant research on g-C3N4-based photocatalysts for viral inactivation by reactive oxidative species generation. An evaluation of the photocatalysis operational parameters affecting viral inactivation kinetics is presented. An overview of the prevailing challenges and sustainable solutions is presented to fill in the existing knowledge gaps. Given the merits of graphitic carbon nitride and the heterogeneous photocatalytic viral inactivation mechanism, we hope that further research will contribute to preventing the ongoing Coronavirus pandemic and future calamities.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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