Graphene quantum dot and iron co-doped TiO2 photocatalysts: Synthesis, performance evaluation and phytotoxicity studies

Carbon and graphene quantum dots based architectonics for efficient aqueous decontamination by adsorption chromatography technique - Current state and prospects

Aquatic ecosystems and potable water are being exploited and depleted due to urbanization and the encouragement of extensive industrialization, which induces the scarcity of pure water. However, current decontamination methods are limited and inefficient. Various innovative remediation strategies with novel nanomaterials have recently been demonstrated for wastewater treatment. Carbon dots (C-dots) and graphene quantum dots (GQ-dots) are the most recent frontiers in carbon nanomaterial-based adsorption studies. C-dots are extremely small (1-10 nm) quasi-spherical carbon nanoparticles (mostly sp3 hybridized carbon), whereas GQ-dots are fragments of graphene (1-20 nm) composed of primarily sp2 hybridized carbon. This article highlights the function of C-dots and GQ-dots with their specifications and characteristics for the efficient removal of organic and inorganic contaminants in water via adsorption chromatography. The alteration of adsorption attributes with the hybrid blending of these dots has been critically analyzed. Moreover, various top-down and bottom-up approaches for synthesizing C-dots and GQ-dots, which ultimately affect their morphology and structure, are described in detail. Finally, we review the research deficit in the adsorption of diverse pollutants, fabrication challenges, low molecular weight, self-agglomeration, and the future of the dots by providing research prospects and selectivity and sensitivity perspectives, the importance of post-adsorption optimization strategies and the path toward scalability at the tail of the article.

Highly Stable Self-Cleaning Paints Based on Waste-Valorized PNC-Doped TiO2 Nanoparticles

Adding photocatalytically active TiO2 nanoparticles (NPs) to polymeric paints is a feasible route toward self-cleaning coatings. While paint modification by TiO2-NPs may improve photoactivity, it may also cause polymer degradation and release of toxic volatile organic compounds. To counterbalance adverse effects, a synthesis method for nonmetal (P, N, and C)-doped TiO2-NPs is introduced, based purely on waste valorization. PNC-doped TiO2-NP characterization by vibrational and photoelectron spectroscopy, electron microscopy, diffraction, and thermal analysis suggests that TiO2-NPs were modified with phosphate (P=O), imine species (R=N-R), and carbon, which also hindered the anatase/rutile phase transformation, even upon 700 °C calcination. When added to water-based paints, PNC-doped TiO2-NPs achieved 96% removal of surface-adsorbed pollutants under natural sunlight or UV, paralleled by stability of the paint formulation, as confirmed by micro-Fourier transform infrared (FTIR) surface analysis. The origin of the photoinduced self-cleaning properties was rationalized by three-dimensional (3D) and synchronous photoluminescence spectroscopy, indicating that the dopants led to 7.3 times stronger inhibition of photoinduced e-/h+ recombination when compared to a benchmark P25 photocatalyst.

Simultaneous preparation of ZnO/rGO composites through Zn(OH)2 decomposition and graphite oxide reduction and their photocatalytic properties

ZnO/reduced graphite oxide (rGO) composites were simultaneously prepared by the thermal reduction of graphite oxide (GO) and the decomposition of Zn(OH)2. The samples were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence, and DRS. Results indicate that Zn(OH)2 was heated and decomposed into ZnO at a low temperature (200 ℃), while GO was reduced to graphene. The synthesized ZnO particles were small and loaded on graphene layers. The ZnO/rGO photocatalysts exhibited excellent photocatalytic activity against methylene blue (MB) under simulated sunlight irradiation. The ZnO/50% rGO photocatalyst showed the best MB photodegradation rate of up to 99.7% within 3 min. Synchronous reaction provided an efficient, simple, and fast preparation method for ZnO/rGO composites, with an excellent solar photocatalytic degradation ability.

Improved photocatalytic decolorization of reactive black 5 dye through synthesis of graphene quantum dots-nitrogen-doped TiO2

Graphene quantum dots (GQDs), a new solid-state electron transfer material was anchored to nitrogen-doped TiO2 via sol gel method. The introduction of GQDs effectively extended light absorption of TiO2 from UV to visible region. GQD-N-TiO2 demonstrated lower PL intensity at excitation wavelengths of 320 to 450 nm confirming enhanced exciton lifespan. GQD-N-TiO2-300 revealed higher surface area (191.91m2 g-1), pore diameter (1.94 nm), TEM particle size distribution (4.88 ± 1.26 nm) with lattice spacing of 0.45 nm and bandgap (2.91 eV). In addition, GQDs incorporation shifted XPS spectrum of Ti 2p to lower binding energy level (458.36 eV), while substitution of oxygen sites in TiO2 lattice by carbon were confirmed through deconvolution of C 1 s spectrum. Photocatalytic reaction followed the pseudo first order reaction and continuous reductions in apparent rate constant (Kapp) with incremental increase in RB5 concentration. Langmuir-Hinshelwood model showed surface reaction rate constants KC = 1.95 mg L-1 min-1 and KLH = 0.76 L mg-1. The active species trapping, and mechanism studies indicated the photocatalytic decolorization of RB5 through GQD-N-TiO2 was governed by type II heterojunction. Overall, the photodecolorization reactions were triggered by the formation of holes and reactive oxygen species. The presence of •OH, 1O2, and O2• during the photocatalytic process were confirmed through EPR analysis. The excellent photocatalytic decolorization of the synthesized nanocomposite against RB5 can be ascribed to the presence of GQDs in the TiO2 lattice that acted as excellent electron transporter and photosensitizer. This study provides a basis for using nonmetal, abundant, and benign materials like graphene quantum dots to enhance the TiO2 photocatalytic efficiency, opening new possibilities for environmental applications.

Recent Advancements in Metal and Non-Metal Mixed-Doped Carbon Quantum Dots: Synthesis and Emerging Potential Applications

In nanotechnology, the synthesis of carbon quantum dots (CQDs) by mixed doping with metals and non-metals has emerged as an appealing path of investigation. This review offers comprehensive insights into the synthesis, properties, and emerging applications of mixed-doped CQDs, underlining their potential for revolutionary advancements in chemical sensing, biosensing, bioimaging, and, thereby, contributing to advancements in diagnostics, therapeutics, and the under standing of complex biological processes. This synergistic combination enhances their sensitivity and selectivity towards specific chemical analytes. The resulting CQDs exhibit remarkable fluorescence properties that can be involved in precise chemical sensing applications. These metal-modified CQDs show their ability in the selective and sensitive detection from Hg to Fe and Mn ions. By influencing their exceptional fluorescence properties, they enable precise detection and monitoring of biomolecules, such as uric acid, cholesterol, and many antibiotics. Moreover, when it comes to bioimaging, these doped CQDs show unique behavior towards detecting cell lines. Their ability to emit light across a wide spectrum enables high-resolution imaging with minimal background noise. We uncover their potential in visualizing different cancer cell lines, offering valuable insights into cancer research and diagnostics. In conclusion, the synthesis of mixed-doped CQDs opens the way for revolutionary advancements in chemical sensing, biosensing, and bioimaging. As we investigate deeper into this field, we unlock new possibilities for diagnostics, therapeutics, and understanding complex biological processes.

Visible Light-Induced Reactive Yellow 145 Discoloration: Structural and Photocatalytic Studies of Graphene Quantum Dot-Incorporated TiO2

Visible light-induced photocatalytic treatment of organic waste is considered a green and efficient route. This study explored the structural and photocatalytic performance of graphene quantum dot (GQD)-incorporated TiO₂ nanocomposites to treat reactive yellow 145 (RY145) dye. For the effective removal of the RY145, efforts were made to better understand the kinetics of the process and optimization of the treatment parameters. Different GQD-doped TiO₂ nanocomposites were synthesized employing the sol-gel method. Physicochemical characteristics of the synthesized nanocomposites were studied through FTIR, XRD, UV-visible spectroscopy, SEM, and EDX. Screening studies were conducted for synthesis and reaction optimization. The results indicated that GQD-TiO₂ significantly enhanced the photocatalytic discoloration for RY145 dye. Among the synthesized nanocomposites, 15GQD-TiO₂ calcined at 300 exhibited 99.3% RY145 discoloration in 30 min under visible light irradiation. Following the pseudo-first-order reaction, the photocatalytic reaction constant K _app progressively declined with an increase in the concentration of RY145. The heterogeneous reaction system conformed to the Langmuir-Hinshelwood isotherm, as indicated by the K _C (1.08 mg L^-1 min^-1) and the K _LH (0.18 L mg^-1) values. O₂ ^•- was found to be the major contributor in GQD-TiO₂-300 to decolorize RY154, while TiO₂ and GQDs played a vital role in generation of electrons and holes. Additionally, after recycling to the seventh cycle, only 9% decline in photocatalytic performance was observed for the synthesized nanocomposite.

Transition metal-doped SnO2 and graphene oxide (GO) supported nanocomposites as efficient photocatalysts and antibacterial agents

In the present work, pristine and transition metal (TM) (W, Ag, Zn)-doped SnO₂ nanocrystals using a facile sol-gel approach were synthesized. The grown products were anchored on graphene oxide (GO) sheets via a simple ultrasonication technique to fabricate binary nanocomposites. The structural, optical, and morphological properties of as-synthesized samples were studied by XRD, FTIR, Raman, EDX, UV-Visible, PL, and FE-SEM. The charge transferability of graphene oxide-based samples was investigated by EIS. The XRD exhibited the TM doping in SnO₂ and the development of GO-based nanocomposite. FTIR data evidenced the existence of the metal-oxygen bonds. Raman spectra presented the optical phonon modes of SnO₂ and the existence of oxygen vacancy defects. FE-SEM images demonstrated the anchoring of particles on the GO sheet, and EDX further approved the existence of desired dopants. The integration of SnO₂ with TM doping remarkably reduced optical bandgap (3.65-3.10 eV), which was further decreased (3.10-2.99 eV) by making composite with GO. The photodegradation results exhibited that GO-based nanocomposites have the higher potential to degrade synthetic dyes (methyl red (MR), and methyl orange (MO) and SnZnO₂/GO have shown superb photocatalytic performance after 80-min sunlight illumination (99.9% MR and 95.0% MO dyes) with the higher rate constant and superior stability up to 6th cycle against MR dye. The grown samples were tested for bacterial disinfection, and SnZnO₂/GO sample showed a higher zone of inhibition towards S. aureus and K. pneumoniae bacteria strains. The greater charge transfer rate and lower recombination of charge carriers in GO-based composites were also observed by EIS and PL analysis. Moreover, the present article ascribed that the photocatalytic and antibacterial properties of bare SnO₂ could be improved by TM doping and fabricating their composite with GO.

Photo-Fenton Degradation of Ciprofloxacin by Novel Graphene Quantum Dots/α-FeOOH Nanocomposites for the Production of Safe Drinking Water from Surface Water

In the current work, novel graphene quantum dots (GQDs)-doped goethite (α-FeOOH) nanocomposites (GQDs/α-FeOOH) were prepared by following a feasible hydrolysis method and applied for ciprofloxacin (CIP) removal. Results showed that the CIP degradation efficiency was significant (93.73%, 0.0566 min−1) in the GQDs/α-FeOOH + H2O2 + Vis system using much lower amounts of H2O2 (0.50 mM), which is 3.9 times the α-FeOOH + H2O2 + Vis system. It was found that •OH, O2•−, and 1O2 were mainly responsible for CIP degradation in the GQDs/α-FeOOH photo-Fenton system. GQDs/α-FeOOH demonstrated broad-spectrum UV–vis-IR responsiveness in the degradation of ciprofloxacin as a function of the doping of GQDs. Additionally, GQDs/α-FeOOH showed outstanding durability (recyclability up to 3 cycles with a lower iron leaking amount, 0.020 mg L−1), a broad range of application pH, and a pretty acceptable catalytic efficacy in a variety of surface water matrices. Overall, GQDs/α-FeOOH have been shown to be an effective photocatalyst for the remediation of emerging contaminants via the workable exploitation of solar energy.

Degradation of Anti-Inflammatory Drugs in Synthetic Wastewater by Solar Photocatalysis

Due to the high number of anti-inflammatory drugs (AIMDs) used by the public health sector in Iraq and distributed all over the country and due to their toxicity, there is a need for an environmental-friendly technique to degrade any wasted (AIMD) present in aquatic ecosystem. The degradation of diclofenac sodium (DCF), ibuprofen (IBN), and mefenamic acid (MFA) in synthetic hospital wastewater were investigated utilizing locally-made Cu-coated TiO2 nanoparticles in a solar-irradiated reactor. Different key variables were studied for their effects on process efficiency, such as loadings of catalyst (C CU-TiO2 = 100–500 mg/L), AIMDs (100 µg/L), pH (4–9), and hydrogen peroxide (CH2O2 = 200–800 mg/L). The results revealed that degradation percentages of 96.5, 94.2, and 82.3%, were obtained for DCF, IBN, and MFA, respectively, using our Cu-coated TiO2 catalyst within 65 min at pH = 9, while other parameters were C CU-TiO2 = 300 mg/L, and CH2O2 = 400 mg/L. The experimental results revealed coupling photocatalysis with solar irradiation as a clean energy source could be utilized for the degradation of toxic pollutants in surface water.