Recent Progress on Metal-Enhanced Photocatalysis: A Review on the Mechanism

Biosynthesized and chemically synthesized Ag/TiO2 nanocomposites: Effect of reaction parameters on synthesis using watermelon rind extract and comparative analysis

This work synthesized Ag/TiO2 nanocomposite via an aqueous reduction method using a green and chemical reducing agent. Citrullus lanatus (watermelon) rind extract (WMRE) and sodium borohydride (NaBH4) were used as the reducing agents during green synthesis and chemical synthesis, respectively. During green synthesis, a pH of 12, a reaction time of 45 min, and an operating temperature of 100 °C yielded the best visible light activity. The biosynthesized and chemically-synthesized Ag/TiO2 were compared using UV-Vis spectroscopy, X-ray fluorescence spectroscopy (XRF), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy-scanning electron microscopy (EDS-SEM) and transmission electron microscopy (TEM). Synthesis using WMRE yielded spherical Ag nanoparticles modified on the surface of TiO2 nanoparticles. The Ag nanoparticles had enhanced monodispersity with an average diameter of 7.48 ± 4.06 nm. Therefore, the developed WMRE green synthesis method provides a simple, less chemical-intensive, and effective alternative to chemical synthesis.

Recent advances and mechanism of plasmonic metal-semiconductor photocatalysis

Benefiting from the unique surface plasmon properties, plasmonic metal nanoparticles can convert light energy into chemical energy, which is considered as a potential technique for enhancing plasmon-induced semiconductor photocatalytic reactions. Due to the shortcomings of large bandgap and high carrier recombination rate of semiconductors, their applications are limited in the field of sustainable and clean energy sources. Different forms of plasmonic nanoparticles have been reported to improve the photocatalytic reactions of adjacent semiconductors, such as water splitting, carbon dioxide reduction, and organic pollutant degradation. Although there are various reports on plasmonic metal-semiconductor photocatalysis, the related mechanism and frontier progress still need to be further explored. This review provides a brief explanation of the four main mechanisms of plasmonic metal-semiconductor photocatalysis, namely, (i) enhanced local electromagnetic field, (ii) light scattering, (iii) plasmon-induced hot carrier injection and (iv) plasmon-induced resonance energy transfer; some related typical frontier applications are also discussed. The study on the mechanism of plasmonic semiconductor complexes will be favourable to develop a new high-performance semiconductor photocatalysis technology.

Schottky Junctions with Bi@Bi2MoO6 Core-Shell Photocatalysts toward High-Efficiency Solar N2-to-Ammonnia Conversion in Aqueous Phase

The photocatalytic nitrogen reduction reaction (NRR) in aqueous solution is a green and sustainable strategy for ammonia production. Nonetheless, the efficiency of the process still has a wide gap compared to that of the Haber-Bosch one due to the difficulty of N2 activation and the quick recombination of photo-generated carriers. Herein, a core-shell Bi@Bi2MoO6 microsphere through constructing Schottky junctions has been explored as a robust photocatalyst toward N2 reduction to NH3. Metal Bi self-reduced onto Bi2MoO6 not only spurs the photo-generated electron and hole separation owing to the Schottky junction at the interface of Bi and Bi2MoO6 but also promotes N2 adsorption and activation at Bi active sites synchronously. As a result, the yield of the photocatalytic N2-to-ammonia conversion reaches up to 173.40 μmol g-1 on core-shell Bi@Bi2MoO6 photocatalysts, as much as two times of that of bare Bi2MoO6. This work provides a new design for the decarbonization of the nitrogen reduction reaction by the utilization of renewable energy sources.

Enhanced photocatalytic performance of ZnO under visible light by co-doping of Ta and C using hydrothermal method

This study attempted to improve the photocatalytic activity of zinc oxide (ZnO) semiconductors in the visible light region by introducing the co-doping of carbon (C) and tantalum (Ta) to ZnO (ZTC) using a simple hydrothermal method with the respective precursors. The obtained uniform ZTC nanoparticles with an average crystal size of 29.30 nm (according to Scherrer's equation) revealed a redshift with a decrease in bandgap (Eg) from 3.04 eV to 2.88 eV, allowing the obtained photocatalyst to absorb the energy of the visible light for photocatalysis. Furthermore, the Zn 2p and Ta 4f core level spectra confirmed the presence of Zn2+ and Ta5+ in the ZTC sample. In addition, the infrared spectra identified hydrogen-related defects (HRDs), while the O 1s spectra indicated the existence of oxygen vacancies (VO). Electrochemical tests revealed improvement in the electron conductivity and charge separation of the obtained materials. To follow, the photocatalytic performance assessment was conducted by varying the C/Zn2+ ratios (5, 10, and 15 mol%) in ZTC samples, the initial RhB concentration (7, 15, and 30 ppm), and the pH of the RhB solution (3.0-10.0). The photodegradation on ZTC samples showed the most effectiveness for a 7 ppm RhB solution with a C/Zn2+ ratio of 10 mol% in the slightly alkaline medium (pH 9.0). Additionally, ZTC also exhibited commendable durability after being reused several times. The nature of RhB photodegradation was proposed and discussed via a mechanism at the end of this work.

Harnessing Renewable Lignocellulosic Potential for Sustainable Wastewater Purification

Utilizing renewable lignocellulosic resources for wastewater remediation is crucial to achieving sustainable social development. However, the resulting by-products and the synthetic process characterized by complexity, high cost, and environmental pollution limit the further development of lignocellulose-based materials. Here, we developed a sustainable strategy that involved a new functional deep eutectic solvent (DES) to deconstruct industrial xylose residue into cellulose-rich residue with carboxyl groups, lignin with carboxyl and quaternary ammonium salt groups, and DES effluent rich in lignin fragments. Subsequently, these fractions equipped with customized functionality were used to produce efficient wastewater remediation materials in cost-effective and environmentally sound manners, namely, photocatalyst prepared by carboxyl-modified cellulose residue, biochar-based adsorbent originated from modified lignin, and flocculant synthesized by self-catalytic in situ copolymerization of residual DES effluent at room temperature. Under the no-waste principle, this strategy upgraded the whole components of waste lignocellulose into high-value-added wastewater remediation materials with excellent universality. These materials in coordination with each other can stepwise purify high-hazardous mineral processing wastewater into drinkable water, including the removal of 99.81% of suspended solids, almost all various heavy metal ions, and 97.09% chemical oxygen demand, respectively. This work provided promising solutions and blueprints for lignocellulosic resources to alleviate water shortages while also advancing the global goal of carbon neutrality.

Photo-enhanced dehydrogenation of formic acid on Pd-based hybrid plasmonic nanostructures

Coupling visible light with Pd-based hybrid plasmonic nanostructures has effectively enhanced formic acid (FA) dehydrogenation at room temperature. Unlike conventional heating to achieve higher product yield, the plasmonic effect supplies a unique surface environment through the local electromagnetic field and hot charge carriers, avoiding unfavorable energy consumption and attenuated selectivity. In this minireview, we summarized the latest advances in plasmon-enhanced FA dehydrogenation, including geometry/size-dependent dehydrogenation activities, and further catalytic enhancement by coupling local surface plasmon resonance (LSPR) with Fermi level engineering or alloying effect. Furthermore, some representative cases were taken to interpret the mechanisms of hot charge carriers and the local electromagnetic field on molecular adsorption/activation. Finally, a summary of current limitations and future directions was outlined from the perspectives of mechanism and materials design for the field of plasmon-enhanced FA decomposition.

Synergistic coupling of interface ohmic contact and LSPR effects over Au/Bi24O31Br10 nanosheets for visible-light-driven photocatalytic CO2 reduction to CO

The challenge of synergistically optimizing different mechanisms limits the further improvement of plasmon-mediated photocatalytic activities. In this work, an Au/Bi24O31Br10 composite, combining an interface ohmic contact and localized surface plasmon resonance (LSPR), is prepared by a thermal reduction method. The LSPR effect induces the local resonance energy transfer effect and the local electric field enhancement effect, while the interface ohmic contact forms a stronger interface electric field. The novel synergistic interaction between the interface ohmic contact and LSPR drives effective charge separation and provides more active sites for the adsorption and activation of CO2 with improved photocatalytic efficiency. The optimized 0.6 wt% Au (5.7 nm) over Bi24O31Br10 nanosheets showed an apparently improved photocatalytic activity without any sacrificial reagents, specifically CO and O2 yields of 44.92 and 17.83 μmol g-1 h-1, and demonstrated superior stability (only lost 6%) after continuous reaction for 48 h, nearly 5-fold enhanced compared to Bi24O31Br10 and a great advantage compared with other bismuth-based photocatalysts.

Single-Molecule Spectroscopy Reveals the Plasmon-Assisted Nanozyme Catalysis on AuNR@TiO2

Gold nanoparticles are frequently employed as nanozyme materials due to their capacity to catalyze various enzymatic reactions. Given their plasmonic nature, gold nanoparticles have also found extensive utility in chemical and photochemical catalysis owing to their ability to generate excitons upon exposure to light. However, their potential for plasmon-assisted catalytic enhancement as nanozymes has remained largely unexplored due to the inherent challenge of rapid charge recombination. In this study, we have developed a strategy involving the encapsulation of gold nanorods (AuNRs) within a titanium dioxide (TiO2) shell to facilitate the efficient separation of hot electron/hole pairs, thereby enhancing nanozyme reactivity. Our investigations have revealed a remarkable 10-fold enhancement in reactivity when subjected to 530 nm light excitation following the introduction of a TiO2 shell. Leveraging single-molecule kinetic analyses, we discovered that the presence of the TiO2 shell not only amplifies catalytic reactivity by prolonging charge relaxation times but also engenders additional reactive sites within the nanozyme's intricate structure. We anticipate that further enhancements in nanozyme performance can be achieved by optimizing interfacial interactions between plasmonic metals and semiconductors.

Metal sulphides and their heterojunctions for photocatalytic degradation of organic dyes-A comprehensive review

Water pollution caused by organic dyes is one of the greatest threats to the ecosystem. The removal of dyes from water has remained a challenge for scientists. Recently, metal sulphides have emerged as a potential candidate for water remediation applications. The efficient charge transportation, greater surface-active sites, and low bandgap of metal sulphides make them an excellent choice of semiconductor photocatalysts for degradation of dyes. This review summarises the potential application of metal sulphides and their heterojunctions for the photocatalytic degradation of organic dyes from wastewater. A detailed study has been presented on the synthesis, basics of photodegradation and heterojunctions and photocatalytic activity. The effect of the use of templates, doping agents, synthesis route, and various other factors affecting the photocatalytic activity of metal sulphides have been summarised in this review. The synthesis techniques, characterisation techniques, mechanism of degradation of organic dyes by Z-scheme heterojunction photocatalyst, reusability and stability of metal sulphides, and the scope of future research are also discussed. This study indicates that Scopus-based core gathered data could be used to give an objective overview of the global dye degradation research from 2008 to 2023 (15 years). All data (articles, authors, keywords, and publications) is compiled in the Scopus database. For the bibliometric study, 1962 papers relevant to dye photodegradation by sulfide-based photocatalysts were found, and this number rises yearly. A bibliometric analysis provides a 15-year evaluation of the state-of-the-art research on the impact of metal sulfide-based photocatalysts on the photodegradation of dyes.

Origin of Superlinear Power Dependence of Reaction Rates in Plasmon-Driven Photocatalysis: A Case Study of Reductive Nitrothiophenol Coupling Reactions

The superlinear dependence of the reaction rate on the power of the excitation light, which may arise from both thermal and nonthermal effects, has been a hallmark of plasmon-driven photocatalysis on nanostructured metal surfaces. However, it remains challenging to distinguish and quantify the thermal and nonthermal effects because even slight uncertainties in measuring the local temperatures at the active surface sites may lead to significant errors in assessing thermal and nonthermal contributions to the overall reaction rates. Here we employ surface-enhanced Raman scattering as a surface-sensitive in situ spectroscopic tool to correlate detailed kinetic features of plasmon-mediated molecular transformations to the local temperatures at the active sites on photocatalyst surfaces. Our spectroscopic results clearly reveal that the superlinearity in the power dependence of the reaction rate observed in a plasmon-driven model reaction, specifically the reductive coupling of para-nitrothiophenol adsorbates on Ag nanoparticle surfaces, originates essentially from photothermal heating rather than nonthermal plasmonic effects.

Enhanced Titania Photocatalyst on Magnesium Oxide Support Doped with Molybdenum

Titania photocatalysts supported on mesoporous MgO carriers doped with Mo(VI) ions were prepared and characterized by XRD, BET nitrogen adsorption, FT-IR, and EPR methods. The photocatalytic activity was evaluated by bleaching an aqueous dye solution in the presence of a dispersed photocatalyst and by bleaching the dry surface of a solid tablet of photocatalyst using rhodamine B and nigrosin as model organic pollutants. It was established that TiO2 photocatalyst based on MgO carrier doped with 1 wt.% Mo(VI) ions, with the ratio of MgO:TiO2 = 1:0.5, possessed the highest activity under UV radiation. The increase in the content of molybdenum up to 10 wt.% leads to the formation of a MoO3 nanophase on the MgO surface, the formation of an isotype n–n heterojunction at the MoO3/TiO2 interface, and photocatalytic activity under the action of visible light.

Synergistic Effect of Iron and Copper Oxides in the Removal of Organic Dyes Through Thermal Induced Catalytic Degradation Process

This study proposes a new method for producing α-Fe2O3–CuO nanocatalyst that is both cost-effective and ecologically benign. The α-Fe2O3–CuO nanocomposite was prepared via moderate thermal oxidative decomposition of copper hexacyanoferrate. Its structure and surface morphology are affirmed via XRD, SEM, FTIR, EDX, TEM, XPS, and VSM. In the presence of H2O2, α-Fe2O3–CuO is employed as a heterogeneous catalyst to stimulate thermally induced degradation of dyes such as direct violet 4, rhodamine b, and methylene blue. The synergistic effect of Fe2O3 and CuO enhanced the catalytic activity of the nanocomposite compared to Fe2O3 and CuO separately. The effectiveness of DV4 degradation is optimized by evaluating multiple reaction parameters. The reaction rate increased substantially with the temperature, revealing its key role in the degradation process. Higher H2O2 levels and the inclusion of inorganic anions like chloride or nitrate also sped up the degradation process. While sulfate and humic acid, particularly at high doses, slowed it. The mechanism of H2O2 activation on α-Fe2O3–CuO is studied. The measurements of chemical oxygen demand and total organic carbon indicate that all dyes are highly mineralized. The remarkable performance and stability of this nanocomposite in removing diverse dyes render it a promising option for wastewater remedy.

Enhanced chiroptic properties of nanocomposites of achiral plasmonic nanoparticles decorated with chiral dye-loaded micelles

The development of circularly polarized luminescence (CPL)-active materials with both large luminescence dissymmetry factor (g_lum) and high emission efficiency continues to be a major challenge. Here, we present an approach to improve the overall CPL performance by integrating triplet-triplet annihilation-based photon upconversion (TTA-UC) with localized surface plasmon resonance. Dye-loaded chiral micelles possessing TTA-UC ability are designed and attached on the surface of achiral gold nanorods (AuNRs). The longitudinal and transversal resonance peaks of AuNRs overlap with the absorption and emission of dye-loaded chiral micelles, respectively. Typically, 43-fold amplification of g_lum value accompanied by 3-fold enhancement of upconversion are obtained simultaneously when Au@Ag nanorods are employed in the composites. More importantly, transient absorption spectra reveal a fast accumulation of spin-polarized triplet excitons in the composites. Therefore, the enhancement of chirality-induced spin polarization should be in charge of the amplification of g_lum value. Our design strategy suggests that combining plasmonic nanomaterials with chiral organic materials could aid in the development of chiroptical nanomaterials.

Biochar for the removal of contaminants from soil and water: a review

Biochar shows significant potential to serve as a globally applicable material to remediate water and soil owing to the extensive availability of feedstocks and conducive physio-chemical surface characteristics. This review aims to highlight biochar production technologies, characteristics of biochar, and the latest advancements in immobilizing and eliminating heavy metal ions and organic pollutants in soil and water. Pyrolysis temperature, heat transfer rate, residence time, and type of feedstock are critical influential parameters. Biochar’s efficacy in managing contaminants relies on the pore size distribution, surface groups, and ion-exchange capacity. The molecular composition and physical architecture of biochar may be crucial when practically applied to water and soil. In general, biochar produced at relatively high pyrolysis temperatures can effectively manage organic pollutants via increasing surface area, hydrophobicity and microporosity. Biochar generated at lower temperatures is deemed to be more suitable for removing polar organic and inorganic pollutants through oxygen-containing functional groups, precipitation and electrostatic attraction. This review also presents the existing obstacles and future research direction related to biochar-based materials in immobilizing organic contaminants and heavy metal ions in effluents and soil.

Graphical Abstract

Application of biochar-based photocatalysts for adsorption-(photo)degradation/reduction of environmental contaminants: mechanism, challenges and perspective

The fast increase of population results in the quick development of industry and agriculture. Large amounts of contaminants such as metal ions and organic contaminants are released into the natural environment, posing a risk to human health and causing environment ecosystem problems. The efficient elimination of contaminants from aqueous solutions, photocatalytic degradation of organic pollutants or the in-situ solidification/immobilization of heavy metal ions in solid phases are the most suitable strategies to decontaminate the pollution. Biochar and biochar-based composites have attracted multidisciplinary interests especially in environmental pollution management because of their porous structures, large amounts of functional groups, high adsorption capacities and photocatalysis performance. In this review, the application of biochar and biochar-based composites as adsorbents and/or catalysts for the adsorption of different contaminants, adsorption-photodegradation of organic pollutants, and adsorption-(photo)reduction of metal ions are summarized, and the mechanism was discussed from advanced spectroscopy analysis and DFT calculation in detail. The doping of metal or metal oxides is the main strategy to narrow the band gap, to increase the generation and separation of photogenerated e−-h+ pairs, to produce more superoxide radicals (·O2−) and hydroxyl radicals (·OH), to enhance the visible light absorption and to increase photocatalysis performance, which dominate the photocatalytic degradation of organic pollutants and (photo)reduction of high valent metals to low valent metals. The biochar-based composites are environmentally friendly materials, which are promising candidates in environmental pollution cleanup. The challenge and perspective for biochar-based catalysts are provided in the end.

Graphical Abstract

Low-temperature plasma induced phosphate groups onto coffee residue-derived porous carbon for efficient U(VI) extraction

For the continuous utilization of nuclear energy and efficient control of radioactive pollution, low-cost materials with high efficient U(VI) removal are of great importance. In this study, low temperature plasma method was applied for the successful modification of O-phosphorylethanolamine (O-PEA) on the porous carbon materials. The produced materials (Cafe/O-PEA) could adsorb U(VI) efficiently with the maximum sorption capacity of 648.54 mg/g at 1 hr, T=298 K, and pH=6.0, much higher than those of most carbon-based composites. U(VI) sorption was mainly controlled by strong surface complexation. From FTIR, SEM-EDS and XPS analyses, the sorption of U(VI) was related to the complexation with -NH₂, phosphate and -OH groups on Cafe/O-PEA. The low temperature plasma method was an efficient, environmentally friendly and low-cost method for surface modification of materials for the effective enrichment of U(VI) from aqueous solutions.

Synthesis of Silver Nanoparticles-Modified Graphitic Carbon Nitride Nanosheets for Highly Efficient Photocatalytic Hydrogen Peroxide Evolution

As a promising metal-free photocatalyst, graphitic carbon nitride (g-C3N4) is still limited by insufficient visible light absorption and rapid recombination of photogenerated carriers, resulting in low photocatalytic activity. Here, we adjusted the microstructure of the pristine bulk-g-C3N4 (PCN) and further loaded silver (Ag) nanoparticles. Abundant Ag nanoparticles were grown on the thin-layer g-C3N4 nanosheets (CNNS), and the Ag nanoparticles decorated g-C3N4 nanosheets (Ag@CNNS) were successfully synthesized. The thin-layer nanosheet-like structure was not only beneficial for the loading of Ag nanoparticles but also for the adsorption and activation of reactants via exposing more active sites. Moreover, the surface plasmon resonance (SPR) effect induced by Ag nanoparticles enhanced the absorption of visible light by narrowing the band gap of the substrate. Meanwhile, the composite band structure effectively promoted the separation and transfer of carriers. Benefiting from these merits, the Ag@CNNS reached a superior hydrogen peroxide (H2O2) yield of 120.53 μmol/g/h under visible light irradiation in pure water (about 8.0 times higher than that of PCN), significantly surpassing most previous reports. The design method of manipulating the microstructure of the catalyst combined with the modification of metal nanoparticles provides a new idea for the rational development and application of efficient photocatalysts.

Synergistic Combination of Charge Carriers and Energy-Transfer Processes in Plasmonic Photocatalysis

Important efforts are currently under way in order to develop further the nascent field of plasmonic photocatalysis, striving for improved efficiencies and selectivities. A significant fraction of such efforts has been focused on distinguishing, understanding, and enhancing specific energy-transfer mechanisms from plasmonic nanostructures to their environment. Herein, we report a synthetic strategy that combines two of the main physical mechanisms driving plasmonic photocatalysis into an engineered system by rationally combining the photochemical features of energetic charge carriers and the electromagnetic field enhancement inherent to the plasmonic excitation. We do so by creating hybrid photocatalysts that integrate multiple plasmonic resonators in a single entity, controlling their joint contribution through spectral separation and differential surface functionalization. This strategy allows us to create complex hybrids with improved photosensitization capabilities, thanks to the synergistic combination of two photosensitization mechanisms. Our results show that the hot electron injection can be combined with an energy-transfer process mediated by the near-field interaction, leading to a significant increase in the final photocatalytic response of the material and moving the field of plasmonic photocatalysis closer to energy-efficient applications. Furthermore, our multimodal hybrids offer a test system to probe the properties of the two targeted mechanisms in energy-related applications such as the photocatalytic generation of hydrogen and open the door to wavelength-selective photocatalysis and novel tandem reactions.

Photocatalytic activity of CuO nanoparticles for organic and inorganic pollutants removal in wastewater remediation

Heterogeneous photocatalysis is a promising technology for eradicating organic, inorganic, and microbial pollutants in water and wastewater remediation. It is a more preferable method to other conventional wastewater treatment approaches on account of its low cost, environmental benignity, ability to proceed at ambient temperature and pressure conditions, and capability to completely degrade pollutants under appropriate conditions into environmentally safe products. In heterogeneous photocatalysis, pollutant removal is mainly induced by in-situ generated reactive radicals and their subsequent attack when energetic radiation impinges on the semiconductor catalyst. As such, for the effective and economical removal of wastewater pollutants, the employed catalyst should have high photonic efficiency, less toxic, abundant, chemically and photochemically stableand visible light active. Copper (II) oxide (CuO) is one among such promising compounds and its photocatalytic performance has been hampered primarily by rapid recombination and slow mobility of photogenerated charge carriers. So, this review provides an overview of the strategies adopted to mitigate the aforementioned drawbacks and also other operational parameters to boost its catalytic activity towards the elimination of toxic organic and inorganic metal ion contaminants in an aqueous media.

Magnetic Metal Oxide-Based Photocatalysts with Integrated Silver for Water Treatment

In this review, the most recent advances in the field of magnetic composite photocatalysts with integrated plasmonic silver (Ag) is presented, with an overview of their synthesis techniques, properties and photocatalytic pollutant removal applications. Magnetic attributes combined with plasmonic properties in these composites result in enhancements for light absorption, charge-pair generation-separation-transfer and photocatalytic efficiency with the additional advantage of their facile magnetic separation from water solutions after treatment, neutralizing the issue of silver’s inherent toxicity. A detailed overview of the currently utilized synthesis methods and techniques for the preparation of magnetic silver-integrated composites is presented. Furthermore, an extended critical review of the most recent pollutant removal applications of these composites via green photocatalysis technology is presented. From this survey, the potential of magnetic composites integrated with plasmonic metals is highlighted for light-induced water treatment and purification. Highlights: (1) Perspective of magnetic properties combined with plasmon metal attributes; (2) Overview of recent methods for magnetic silver-integrated composite synthesis; (3) Critical view of recent applications for photocatalytic pollutant removal.

Combined Experimental and Theoretical Investigation on Formation of Size-Controlled Silver Nanoclusters under Gas Phase

Metallic nanoclusters (NCs) have been predicted to achieve the best Surface-Enhanced Raman Scattering (SERS) due to the controllable amount of atoms and structures in NCs. The Local Surface Plasmon Resonance (LSPR) effect on silver metal NCs (Agn) enables it to be a promising candidate for manipulating the LSPR peak by controlling the size of NCs, which in turn demands a full understanding of the formation mechanism of Agn. Here, we apply an extended Smoluchowski rate equation coupled with a fragmentation scheme to investigate the growth of size-selected silver NCs generated via a modulated pulsed power magnetron sputtering (MPP-MSP). A temperature-dependent fragmentation coefficient D is proposed and integrated into the rate equations. The consistency between the computational and experimental results shows that in relative low peak power (Pp≤800 W), the recombination of cation and anion species are the dominant mechanism for NC growth. However, in the higher Pp region (≥800 W), the fragmentation mechanism becomes more impactful, leading to the formation of smaller NCs. The scanning electron microscopy observation shows the Ag36 is successfully soft-landed and immobilized on a strontium titanate crystal, which facilitates the application of the Agn/STO to the SERS research.

Efficient Selective Removal of Radionuclides by Sorption and Catalytic Reduction Using Nanomaterials

With the fast development of industry and nuclear energy, large amounts of different radionuclides are inevitably released into the environment. The efficient solidification or elimination of radionuclides is thereby crucial to environmental pollution and human health because of the radioactive hazardous of long-lived radionuclides. The properties of negatively or positively charged radionuclides are quite different, which informs the difficulty of simultaneous elimination of the radionuclides. Herein, we summarized recent works about the selective sorption or catalytic reduction of target radionuclides using different kinds of nanomaterials, such as carbon-based nanomaterials, metal-organic frameworks, and covalent organic frameworks, and their interaction mechanisms are discussed in detail on the basis of batch sorption results, spectroscopy analysis and computational calculations. The sorption-photocatalytic/electrocatalytic reduction of radionuclides from high valent to low valent is an efficient strategy for in situ solidification/immobilization of radionuclides. The special functional groups for the high complexation of target radionuclides and the controlled structures of nanomaterials can selectively bind radionuclides from complicated systems. The challenges and future perspective are finally described, summarized, and discussed.

Deposition of Size-Selected Gold Nanoclusters onto Strontium Titanate Crystals for Water Splitting under Visible Light

Using a modulated pulse power magnetron sputtering (MPP-MSP) coupled with a quadrupole mass spectrometer (Q-MS), intensive size-selected gold nanoclusters (Aun) ranging from n = 5 to 40 in size are synthesized and soft landed onto a strontium titanate (STO) crystal surface as a co-catalyst for photocatalytic water splitting. The photocatalytic reactivity of the Aun/STO is investigated by measuring the photocurrent density of the sample under visible light radiation. It is found that the Aun co-catalysts enable the visible light response of the Aun/STO photocatalyst. The photocurrent density is sensitively dependent on the size of the Aun on the STO, and Au16 exhibits its maximum photocurrent under visible light. The underlying physics of the size-specific photocurrent are explained in terms of the size-dependent electron affinity of Aun.

Synthesis of carbon-based nanomaterials and their application in pollution management

With the fast development of industry, large amounts of organic and inorganic pollutants are inevitably released into the natural environment, which results in the pollution of the environment and are thereby dangerous to human health. The efficient elimination of these pollutants is crucial to environment protection and human health. The high sorption capacity of carbon-based materials and high photocatalytic ability of carbon-based composites result in the application of carbon-based materials in environmental pollution cleanup. In this review article, we summarized recent studies on the synthesis of carbon-based materials, and their application in the sorption of organic and inorganic pollutants, the photocatalytic degradation of organic pollutants, and the in situ photocatalytic reduction-solidification of heavy metal ions. The sorption method is useful to remove pollutants from aqueous solutions. The sorption-photocatalytic degradation of organic pollutants is applicable, especially at low concentrations, whereas the catalytic reduction of metal ions is the best method for the in situ immobilization of high valent metal ions under complicated conditions. The interaction mechanism is discussed using advanced spectroscopy analysis and theoretical calculations, and at the end the challenges in the future are described.

Flow photocatalysis system-based functionalized graphene oxide-ZnO nanoflowers for degradation of a natural humic acid

The functionalized graphene oxide-ZnO (fGO/ZnO) nanoflower composites have been studied as a photocatalyst material for flow photodegradation of humic acid (HA) in real samples. The fGO/ZnO nanoflower was prepared via hydrothermal methods. The chemical and physical properties of the synthesized photocatalyst have been carried out by several techniques, including X-ray diffraction (XRD), scanning electron microscope-energy-dispersive spectrometer (SEM-EDS), Fourier transform infrared (FTIR), and UV-Vis spectrophotometer. The photocatalytic study of degradation of HA by flow system is reported. The optimum condition for degradation was found at pH 4.0, a flow rate of 1 mL min^-1, and a light intensity of 400 mW cm^-2. The degradation efficiency of HA also was influenced by several anion or cation concentration ratios on the system. This method was applied for the degradation of HA in extracted natural HA from the soil, and the efficiency achieved at 98.5%. Therefore, this research provides a low-cost, fast, and reusability method for HA degradation in the environment.

Recent advances in metal-organic framework membranes for water treatment: A review

Among many separation membranes reported to date, the favorable polymer affinity and unique physio-chemical performances of metal-organic frameworks (MOFs) including ultra-high surface area, regular and highly controlled porosity have drawn widespread attention in industrial and academic communities. In this comprehensive review, the developmental timeline of MOF containing membranes for water treatment were clarified. The removal efficiencies, elimination mechanisms, as well as possible influencing factors of various MOF containing membranes that applied to water treatment were systematically summarized. The excellent removal performances of MOF containing membranes for various pollutants were determined by the size-exclusion, π-π stacking interaction, electrostatic interaction, hydrogen bonding and so on. Since the progress of engineered MOF containing membranes for practical wastewater treatment applications lags, we further analyzed the potential environmental application of MOF containing membranes from four aspects (stability of MOFs, antifouling performance of membranes, compatibility between MOF fillers and polymer matrix, dispersity of MOF nanoparticles in matrix), hoping to provide some meaningful insights.

Fabrication and Characterization of Co-Doped Fe2O3 Spindles for the Enhanced Photo-Fenton Catalytic Degradation of Tetracycline

Co-doped Fe2O3 spindles with different Co contents were successfully fabricated by a facile one-step hydrothermal method. The crystalline structure, morphology, optical properties, and chemical state of the as-prepared catalysts before and after photo-Fenton reaction were characterized. Co2+ incorporated into the Fe2O3 lattice was confirmed by the above characterizations. Also, the photocatalytic and photo-Fenton catalytic performances of the samples were evaluated by the degradation of tetracycline (TC) under visible light irradiation in the absence/presence of H2O2. The results demonstrated that Co-doped Fe2O3 spindles exhibited better catalytic degradation performance in comparison with single Fe2O3 spindles, and the sample of Co(5%)-Fe2O3 spindles displayed the highest activity and best stability. The improvement of photo-Fenton activity might be attributed to two reasons: On the one hand, Co-doped Fe2O3 spindles not only formed the Fe vacancies to reduce the band gap but also could build up an internal electric field, which inhibits electron/hole pair recombination and facilitates the transfer of photoexcited charge carriers. On the other hand, the intrinsic Co2+/Co3+ redox cycling can accelerate the circulation between Fe2+ and Fe3+ in Co(5%)-Fe2O3 spindles to facilitate H2O2 consumption and produce more ·OH radicals for TC degradation.

Facile and Green Synthesis of Silver Quantum Dots Immobilized onto a Polymeric CTS-PEO Blend for the Photocatalytic Degradation of p-Nitrophenol

Immobilization of inorganic metal quantum dots (especially, noble transition metals) onto organic polymers to synthesize nanometal-polymer composites (NMPCs) has attracted considerable attention because of their advanced optical, electrical, catalytic/photocatalytic, and biological properties. Herein, novel, highly efficient, stable, and visible light-active NMPC photocatalysts consisting of silver quantum dots (Ag QDs) immobilized onto polymeric chitosan-polyethylene oxide (CTS-PEO) blend sheets have been successfully prepared by an in situ self-assembly facile casting method as a facile and green approach. The CTS-PEO blend polymer acts as a reducing and a stabilizing agent for Ag QDs which does not generate any environmental chemical pollutant. The prepared x wt % Ag QDs/CTS-PEO composites were fully characterized through X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), thermogravimetric analysis, and UV/visible spectroscopy. The characterization results indicated the successful synthesis of the Ag QDs/CTS-PEO composites by the interactions and complexation between x wt % Ag QDs and CTS-PEO blend sheets. TEM images revealed small granules randomly distributed onto the CTS-PEO blend sheets, indicating the immobilization of Ag QDs onto CTS-PEO composites. The presence of a surface plasmon resonance (SPR) band and the shifting of the absorption edge toward higher wavelengths in the UV/vis spectra indicated the formation of x wt % Ag QDs/CTS-PEO composites. The Ag QDs in the polymeric blend matrix led to remarkable enhancement in the optical, thermal, electrical, and photocatalytic properties of x wt % Ag QDs/CTS-PEO composites. The photocatalytic efficiency of the prepared composites was evaluated by the photodegradation of p-nitrophenol (PNP) under simulated sunlight. The maximum photocatalytic degradation reached 91.1% efficiency within 3 h for the 12.0 wt % Ag QDs/CTS-PEO photocatalyst. Generally, the Ag QDs immobilized onto CTS-PEO blend composites significantly enhance the SPR effect and the synergistic effect and reduce the band gap, leading to a high photocatalytic activity.

Highly Efficient Flower-Like Graphene Quantum Dots-Based Fuschin Photocatalyst for Selective NAD(P)H Cofactor Regeneration Under Solar Light Irradiation

To meet the energy demands artificial photosynthesis is playing the most promising role these days. Using sunlight directly in a manner that can provide useful chemicals is a sustainable means of generating energy. Studies are going on in this context to make better and effective photocatalyst. In this paper, we study the synthesis of flower-like graphene quantum dots-based fuschin (GQDF) photocatalyst from lemon_, which is created by a green and sustainable process that is effective and environment friendly. The UV-visible spectra of prepared GQDF showed a high molar extinction coefficient. A flower-like GQDF photocatalyst has better catalytic efficiency for the selective creation and regeneration of the NAD(P)H cofactor. A newly designed flower-like GQDF photocatalyst is used as one of its most effective photocatalysts as they have several additional applications in the removal of CO₂ and aqueous contaminants like heavy metals.