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Correction for 'Carbon quantum dots (CQDs)-modified polymers: a review of non-optical applications' by Zeeshan Latif et al., Nanoscale, 2024, 16, 2265-2288, https://doi.org/10.1039/D3NR04997C.

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Carbon quantum dots (CQDs) are a promising candidate to replace metal-based additives for polymer reinforcement and functionalization. Specifically, vast interest in CQDs for polymer functionalization stems from their cost effectiveness, sustainable organic precursors, and their non-toxicity. Although several reviews of optical devices based on CQDs have been reported, this mini-review covers the non-optical aspects of CQD-polymer composites. Applications of CQD-modified polymers for smart devices, mechanical reinforcement, textile surface-modification methods, membranes, protective coatings, and thermal resistance are summarized. The synthesis method of CQDs, their dispersion in a polymer matrix and the underlying mechanisms related to the enhanced performance of composites are outlined. Unlike nano-reinforcements, CQDs are self-stabilized and offer an extremely high surface area, which significantly alters the polymer properties at a 1-2% concentration. Finally, a comparative analysis of recent advances in CQD-polymer composites, their problems, and future directions are discussed.

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Nanobubble and ultrasonic cavitation were applied to support and prolong oxidation reactions of ozonation. Nanobubbles increased ozone dissolution by a factor of 16 due to low buoyancy, high surface area, and stability in water. Hydroxyl radicals generated by ultrasonic cavitation produced hydrogen peroxide rather than recombining due to additional oxygen atoms supplied by the nanobubbles. The generated hydrogen peroxide formed hydroperoxyl ions that reacted with ozone to generate hydroxyl radicals. The process achieved improvements in both the loss of emitted ozone and radical recombination. Rhodamine B decomposition was used to gauge the effectiveness of the process, with the highest rhodamine B decomposition evident at a high initial pH and power and a frequency of 132 kHz as revealed in ultrasonic experiments. The process achieved more than 99% of the rhodamine B decomposition in 20 min under the most efficient conditions. The generation of hydrogen peroxide exhibited tendencies similar to those of rhodamine B decomposition, supporting the proposed mechanism. An ozonation process combined with nanobubble and ultrasonic cavitation can therefore sustain oxidizing power using continuous dissolution by nanobubbles and successive radical generation caused by hydrogen peroxide generated by cavitation.

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A new functional composite was synthesized in this study comprising magnetic-cored dendrimer (MCD) modified with citric acid (CA), succinic acid (SA), and vanillic acid (VA) terminal groups. The CA-MCD, SA-MCD, and VA-MCD exhibited average particle size of 8-18 nm and superparamagnetic behavior. Adsorption potential of the composite was assessed by monitoring methylene blue (MB) removal from contaminated water. The CA-MCD attained adsorption equilibrium in 30 min while SA-MCD and VA-MCD achieved equilibrium in 60 min. The Langmuir model better fitted the adsorption results than the Freundlich model, indicating a monolayer mode of MB adsorption on the composite. Maximum adsorption capacity of CA-MCD, SA-MCD, and VA-MCD was 216.30 mg/g, 184.29 mg/g, and 196.58 mg/g, respectively. The CA-MCD exhibited best adsorption performance by removing 99% MB at pH = 11. In reusability experiments, the CA-MCD, SA-MCD, and VA-MCD maintained over 90% MB adsorption for both 15 mg/L and 50 mg/L solutions in the third cycle. Overall, the organic acid-functionalized MCDs with high adsorption capacity and reusability potential showed utility for practical application for wastewater decontamination.

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Photocatalyst immobilization on support materials is essential for large-scale applications. Here, we describe growth of a p-n junction catalyst (NiO/TiO2) on a stainless-steel mesh (SSM) support using a facile hydrothermal method. The morphological superiority of the composite over previously reported NiO/TiO2 catalysts was probed using scanning and transmission electron microscopy. Flower petal-like NiO grew uniformly on SSM, which was evenly covered by TiO2 nanoparticles. Theoretical and experimental X-ray diffraction patterns were compared to analyze the development of the composite during various stages of synthesis. The photocatalytic activity of a powdered catalyst and SSM@catalyst was compared by measuring bisphenol A (BPA) degradation. SSM@NiO/TiO2 achieved the highest rate of BPA degradation, removing 96% of the BPA in 120 min. Scavenging experiments were used to investigate the charge separation and degradation mechanism. SSM@NiO/TiO2 showed excellent reusability potential, achieving and sustaining 91% BPA removal after 10 rounds of cyclic degradation. Reusability performance, composite resilience, apparent quantum yields, and figures of merit suggest that SSM@NiO/TiO2 has excellent utility for practical applications.

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We reviewed washing of radioactive Cs-contaminated concrete and soil based on the fate of Cs in concrete and soil, including sorption materials for treatment of supernatant solution. In non-aged cement materials (the calcium silicate hydration (C-S-H) phase), it was possible to decontaminate Cs using ion exchange with monovalent cations, such as NH4+. The clay components in the soil and aggregates were important factors in optimization of the efficiency and mechanism for Cs decontamination with washing solution. The parameters (reagent component, pH, and temperature) of the washing solution should be determined considering soil mineral type (here, weathered biotite (WB) with vermiculite), since monovalent cations such as NH4+ and K+ can inhibit Cs decontamination due to collapse of the hydrated and expanded interlayer regions with cation exchange. In this case, hydrothermal treatment or H2O2 dosing was necessary to expand the collapsed interlayer region for Cs removal by washing with cation exchange or organic acids. Acid and a chelating agent significantly enhanced Cs-release with dissolution of the adsorbent layer containing iron and aluminum oxides. The important characteristics of important and emerging sorption materials for treatment of the radioactive Cs-contaminated supernatant after washing treatment are discussed. Sorbents for treatment of washing supernatant are divided in to two main categories. Clay minerals, metal hexacyanoferrates, and ammonium molybdophosphates are discussed in the inorganic class of materials. Hypercrosslinked polymers, supramolecular sorbents, carbon nanotubes, and graphene oxide are covered in the carbon-based sorbents for Cs removal from water.

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Here, we propose an alveoli-inspired catalyst to address the susceptibility of photocatalytic air oxidation systems to fluctuations in volatile organic contaminant (VOC) loads. An alveoli structure was fabricated by covering ZnO nanorods grown on a stainless-steel mesh (SSM) with a porous NiMoO4/C3N4 layer. The alveoli catalyst regulates VOC mass transfer from the air to the catalyst surface using air pockets that capture VOC molecules by diffusion driven by a concentration gradient. Air pockets act as localized reservoirs of molecules that prevent scarcity and congestion at the catalyst surface at low and high VOC loads, respectively. The presence of air pockets in the catalyst assembly and its potential to capture VOC was confirmed by a distinct bimodal adsorption configuration. A ZnO/NiMoO4/C3N4@SSM (ZNC@SSM) catalyst with air pockets achieved a high degree of toluene adsorption (6.1 µmol·m-2). Toluene selectivity of ZnO controlled the delivery of molecules to active catalyst sites, resulting in 95% toluene conversion in 90 min. Synergetic toluene adsorption in air pockets and degradation on catalytic sites helped achieve a quantum yield of 4.14 × 10-05 molecules/photon. A figure of merit reflecting fundamental system parameters was compared with previous photocatalytic systems to evaluate the practicality of ZNC@SSM.

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A novel nanocomposite of stainless-steel nanotubes with graphene quantum dots (SSNT@GQD) was synthesized to degrade phenanthrene photocatalytically under visible light. Photocatalytic performance of bare stainless-steel nanotubes (SSNT) is not satisfactory due to the fast recombination of photoinduced electron-hole pairs. This phenomenon was effectively overcome by inclusion of GQDs and addition of persulfate as an external electron acceptor to improve charge separation. The pseudo-first-order rate constant of phenanthrene degradation by SSNT@GQD with persulfate under visible light was 0.0211 ± 0.0006 min-1, about 42 times higher than that of persulfate and visible light, 0.0005 ± 0.0000 min-1. Effects of different water quality parameters were investigated, including levels of initial pH, natural organic matters, bicarbonate, and chloride. Sulfate radicals, superoxide radicals, and photo-generated holes were the key reactive species in this photocatalytic process. Based on the analysis of intermediates using purge and trap-GC-MS, possible photocatalytic degradation pathways of phenanthrene in this process were proposed. The SSNT@GQD showed high figure of merit (99.5 without persulfate and 78.7 with persulfate) and quantum yield (1.56 × 10-5 molecules photon-1 without persulfate and 4.64 × 10-5 molecules photon-1 with persulfate), indicating that this material has excellent potential for practical photocatalysis applications.

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Nitrogen-doped graphene quantum dots (NGQDs) are a diverse organic catalyst, competitive with other metallic catalysts due to their low cost, high stability, biocompatibility, and eco-friendliness. Highly functional multi-edge surfaces of NGQDs play a key role in imparting superb photocatalytic and electrocatalytic activity. However, when coating NGQDs by conventional techniques, such surfaces are not exposed for catalysis, due to the unwanted overlap of NGQDs sheets. To avoid this issue, here we propose a facile technique to orient NGQDs in a three-dimensional (3D) self-assembled foam-like structure, over reduced graphene oxide coated woven carbon fabric. This 3D assembled structure provides highly exposed active surfaces, which are readily available for catalytic reactions: however, in the conventional uniformly coated NGQDs layer, catalytic activity was limited by complex diffusion. The superb catalytic activity of the assembled NGQDs was utilized for the degradation of organic pollutant (methylene blue dye) from water. Additionally, the proposed electrode revealed much higher electrocatalytic activity than the rare Pt catalyst, owing to the easy diffusion of electrolyte and fast quenching of charges through the porous structure. The assembled NGQDs showed 50% higher photocatalytic degradation compared to uniformly coated NGQDs, which was further accelerated (50%) by application of the biased potential of 2 V; i.e. photo-electrocatalysis. The novel photo-electrocatalytic electrode offers high conductivity, stability, and flexibility, which make this complete carbon electrode highly attractive for other catalytic applications such as fuel cells, supercapacitors, and water splitting.

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Immobilization of nanocomposites without compromising their photocatalytic performance is a challenging task. Here, we report a new method that utilizes analogous crystal orientations and similarities in interplanar spacings for photocatalyst immobilization. The photocatalyst rGO/ZrO2/Ag3PO4 was synthesized using a green hydrothermal method. A primary layer of ZrO2 and a secondary layer of rGO/ZrO2/Ag3PO4 composite were deposited on a fluorine-doped tin oxide (FTO) substrate. The analogous crystal orientation and interplanar spacing of ZrO2 between the two layers resulted in composite immobilization on the FTO substrate. X-ray diffraction analysis confirmed that ZrO2 growth occurred along the same crystal planes in both layers. The film exhibited a low band gap energy (2.6 eV) and excellent light absorption. Photocatalytic performance achieved 92% para-nitrophenol degradation in 150 min. The degradation performance of this immobilization method was 43% higher than those of rGO/ZrO2/Ag3PO4 films deposited with conventional binder approaches. The quantum yield of the system was 3.46 × 10-5 molecules·photon-1. Finally, a figure of merit based on different parameters was determined and compared with previous results to assess the practicality of this system.

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Synergy between surface adsorption and photocatalysis is key for effective contaminant degradation in the liquid phase. Herein, we report a heterojunction photocatalyst of reduced graphene oxide (rGO)/zirconium dioxide (ZrO2)/silver phosphate (Ag3PO4) that incorporates this synergy for 4-nitrophenol (PNP) removal. Compared with other photocatalyst combinations, ZrO2 and Ag3PO4 coupling generates reactive species with greater degradation potential. ZrO2 and rGO were synthesized by a green approach using a one-step hydrothermal reaction in ethanol-water. The growth of rGO/ZrO2 and Ag3PO4 were accomplished and the functions of each part were well developed together. The rGO/ZrO2/Ag3PO4 composite exhibited enhanced light absorption and a low band gap energy (2.3 eV) owing to rGO and Ag3PO4 integration. The composite's photocatalytic activity was much higher than that of ZrO2, Ag3PO4, or ZrO2/Ag3PO4. The maximal adsorption of PNP was 26.88 mg/g, and a pseudo-first-order model described the PNP degradation kinetics (k = 0.034 min-1). Synergy between the three components resulted in 97% PNP removal in 90 min, and even after five cycles, 94% PNP removal was obtained. The quantum yield of the system (7.31 × 10-5 molecules/photon) was compared with those in previous reports to assess the photocatalytic performance and energy requirements.