Synthesis of magnetic carbon nanodots for recyclable photocatalytic degradation of organic compounds in visible light

Fabrication of a reusable carbon quantum dots (CQDs) modified nanocomposite with enhanced visible light photocatalytic activity

In awareness of industrial dye wastewater, carbon quantum dots (CQDs) and cobalt zinc ferrite (CZF) nanocomposites were synthesised for the making of carbon quantum dots coated cobalt zinc ferrite (CZF@CQDs) nanophotocatalyst using oxidative polymerization reaction. The results of TEM, zeta potential value, and FTIR confirm highly dispersed 1-4 nm particles with the - 45.7 mV carboxylic functionalized surface of CQDs. The results of the synthesised CZF@CQDs photocatalyst showed an average particle size of ~ 15 nm according to TEM, SEM, and XRD. The photocatalyst showed a 1.20 eV band gap, which followed the perfect visible light irradiation. TGA and DTA revealed the good thermal stability of the nanophotocatalyst. VSM was carried out, and the saturation magnetisations for CZF and CZF@CQDs were 42.44 and 36.14 emu/g, respectively. A multipoint study determined the BET-specific surface area of the CZF@CQDs photocatalyst to be 149.87 m2/g. Under visible light irradiation, the final CZF@CQDs nanophotocatalyst demonstrated remarkable efficiency (~ 95% within 25 min) in the photocatalytic destruction of Reactive Blue 222 (RB 222) and Reactive Yellow 145 (RY 145) dyes, as well as mechanical stability and recyclability. Even after the recycling of the degradation study, the nanophotocatalyst efficiency (~ 82%, 7th cycles) was predominantly maintained. The effects of several parameters were also investigated, including initial dye concentration, nanophotocatalyst concentration, CQD content, initial pH of the dye solution, and reaction kinetics. Degradation study data follow the first-order reaction rate (R2 > 0.93). Finally, a simple and low-cost synthesis approach, rapid degradation, and outstanding stability of the CQD-coated CZF nanophotocatalyst should make it a potential photocatalyst for dye wastewater treatment.

Chemical- and green-precursor-derived carbon dots for photocatalytic degradation of dyes

Rapid industrialization and untreated industrial effluents loaded with toxic and carcinogenic contaminants, especially dyes that discharge into environmental waters, have led to a rise in water pollution, with a substantial adverse impact on marine life and humankind. Photocatalytic techniques are one of the most successful methods that help in degradation and/or removal of such contaminants. In recent years, semiconductor quantum dots are being substituted by carbon dots (CDs) as photocatalysts, due to the ease of formation, cost-effectiveness, possible sustainability and scalability, much lower toxicity, and above all its high capacity to harvest sunlight (UV, visible, and near infrared) through electron transfer that enhances the lifetime of the photogenerated charge carriers. A better understanding between the properties of the CDs and their role in photocatalytic degradation of dyes and contaminants is required for the formation of controllable structures and adjustable outcomes. The focus of this review is on CDs and its composites as photocatalysts obtained from different sustainable green as well as chemical precursors. Apart from the synthesis, characterization, and properties of the CDs, the study also highlights the effect of different parameters on the photocatalytic properties of CDs and their composites for catalytic dye degradation mechanisms in detail. Besides the present research development in the field, potential challenges and future perspectives are also presented.

Magnetic Carbon Quantum Dots/Iron Oxide Composite Based on Waste Rice Noodle and Iron Oxide Scale: Preparation and Photocatalytic Capability

To provide an economical magnetic photocatalyst and introduce an innovative approach for efficiently utilizing discarded waste rice noodle (WRN) and iron oxide scale (IOS), we initially converted WRN into carbon quantum dots (CQDs) using a hydrothermal method, simultaneously calcining IOS to obtain iron oxide (FeOx). Subsequently, we successfully synthesized a cost-effective, magnetic CQDs/FeOx photocatalytic composite for the first time by combining the resulting CQDs and FeOx. Our findings demonstrated that calcining IOS in an air atmosphere enhanced the content of photocatalytically active α-Fe2O3, while incorporating WRN-based CQDs into FeOx improved the electron-hole pair separation, resulting in increased O2 reduction and H2O oxidation. Under optimized conditions (IOS calcination temperature: 300 °C; carbon loading: 11 wt%), the CQDs/FeOx composite, utilizing WRN and IOS as its foundation, exhibited exceptional and reusable capabilities in photodegrading methylene blue and tetracycline. Remarkably, for methylene blue, it achieved an impressive degradation rate of 99.30% within 480 min, accompanied by a high degradation rate constant of 5.26 × 10-3 min-1. This composite demonstrated reusability potential for up to ten photocatalytic cycles without a significant reduction in the degradation efficiency, surpassing the performance of IOS and FeOx without CQDs. Notably, the composite exhibited strong magnetism with a saturation magnetization strength of 34.7 emu/g, which enables efficient and convenient recovery in photocatalytic applications. This characteristic is highly advantageous for the large-scale industrial utilization of photocatalytic water purification.

A sustainable remediation of Congo red dye using magnetic carbon nanodots and B. pseudomycoides MH229766 composite: mechanistic insight and column modelling studies

In the present investigation, a biocomposite, magnetic carbon nanodot immobilized Bacillus pseudomycoides MH229766 (MCdsIB) was developed and consequently characterized using SEM-EDX, FTIR, XRD, and VSM analyses to effectively biotreat hazardous Congo red (CR) dye present in water bodies. The adsorptive efficiency of MCdsIB for the detoxification of CR from wastewater was investigated both in batch and column schemes. Optimum batch parameters were found as pH 3, 50 mg L-1 dye concentration, 150 min equilibrium time, and 2 g L-1 MCdsIB dosage. The Freundlich isotherm model best fit the experimental data, and the maximum adsorption capacity of MCdsIB was observed as 149.25 mg g-1. Kinetic data were in accordance with the pseudo-second-order model where the adsorption rate reduced with the rise in the initial concentration of dye. Intra-particle diffusion was discovered as the rate-limiting step following 120 min of the adsorption process. Furthermore, despite being used continually for five consecutive cycles, MCdsIB demonstrated excellent adsorption capacity (> 85 mg g-1), making it an outstanding recyclable material. The CR dye was efficiently removed in fixed-bed continuous column studies at high influent CR dye concentration, low flow rate, and high adsorbent bed height, wherein the Thomas model exhibited an excellent fit with the findings acquired in column experiments. To summarize, the current study revealed the effectiveness of MCdsIB as a propitious adsorbent for CR dye ouster from wastewater.

State-of-the-art developments in carbon quantum dots (CQDs): Photo-catalysis, bio-imaging, and bio-sensing applications

Carbon quantum dots (CQDs), the intensifying nanostructured form of carbon material, have exhibited incredible impetus in several research fields such as bio-imaging, bio-sensing, drug delivery systems, optoelectronics, photovoltaics, and photocatalysis, thanks to their exceptional properties. The CQDs show extensive photonic and electronic properties, as well as their light-collecting, tunable photoluminescence, remarkable up-converted photoluminescence, and photo-induced transfer of electrons were widely studied. These properties have great advantages in a variety of visible-light-induced catalytic applications for the purpose of fully utilizing the energy from the solar spectrum. The major purpose of this review is to validate current improvements in the fabrication of CQDs, characteristics, and visible-light-induced catalytic applications, with a focus on CQDs multiple functions in photo-redox processes. We also examine the problems and future directions of CQD-based nanostructured materials in this growing research field, with an eye toward establishing a decisive role for CQDs in photocatalysis, bio-imaging, and bio-sensing applications that are enormously effective and stable over time. In the end, a look forward to future developments is presented, with a view to overcoming challenges and encouraging further research into this promising field.

Optical properties and photoactivity of carbon nanodots synthesized from olive solid wastes at different carbonization temperatures

Carbon nanodots (CNDs) have many fascinating properties, such as optical properties (UV-Visible absorption and fluorescence emission), which make them good candidates in many applications, such as photocatalysts for the degradation of several organic pollutants. This study aims to synthesize CNDs from olive solid wastes at different carbonization temperatures from 300 to 900 °C and study the effect on the optical properties of the CNDs, such UV-Vis, fluorescence, quantum yield, and energy bandgap, in addition to the influence on the photoactivity of the CNDs as photocatalysts for the degradation of methylene blue (MB). CNDs were prepared from olive solid wastes (OSWs) by pyrolysis at different temperatures (300-900 °C) for conversion to carbonized material, and then oxidized chemically in the presence of hydrogen peroxide (H2O2). It was found that an increase in the carbonization temperature of the OSWs leads to an increase in the product yield with a maximum value at 500 °C, and it then decreased dramatically. On the other hand, a decrease in fluorescence due to the diminishment of oxygen groups and the destruction of the surface of the CNDs was observed. The higher quantum yield (5.17%) and bandgap (2.77 eV) were achieved for CNDs prepared from OSWs that carbonized at 300 °C. The rate and degradation efficiency of MB were studied with the different synthesized CNDs, and it was found that an increase in the carbonization temperature leads to a decrease in the rate and degradation efficiency of MB, with the highest degradation rate of 0.0575 min-1 and degradation efficiency of 100% after 120 minutes of light irradiation being realized for the sample carbonized at 300 °C.

Facile Synthesis of "Boron-Doped" Carbon Dots and Their Application in Visible-Light-Driven Photocatalytic Degradation of Organic Dyes

Carbon dots (C-dots) were facilely fabricated via a hydrothermal method and fully characterized. Our study shows that the as-synthesized C-dots are nontoxic, negatively charged spherical particles (average diameter 4.7 nm) with excellent water dispersion ability. Furthermore, the C-dots have a rich presence of surface functionalities such as hydroxyls and carboxyls as well as amines. The significance of the C-dots as highly efficient photocatalysts for rhodamine B (RhB) and methylene blue (MB) degradation was explored. The C-dots demonstrate excellent photocatalytic activity, achieving 100% of RhB and MB degradation within 170 min. The degradation rate constants for RhB and MB were 1.8 × 10⁻² and 2.4 × 10⁻² min⁻¹, respectively. The photocatalytic degradation performances of the C-dots are comparable to those metal-based photocatalysts and generally better than previously reported C-dots photocatalysts. Collectively considering the excellent photocatalytic activity toward organic dye degradation, as well as the fact that they are facilely synthesized with no need of further doping, compositing, and tedious purification and separation, the C-dots fabricated in this work are demonstrated to be a promising alternative for pollutant degradation and environment protection.