Carbon quantum dots: An environmentally friendly and valued approach to sludge disposal

Carbon quantum dots for sustainable energy: enhancing electrocatalytic reactions through structural innovation

Carbon quantum dots (CQDs) have emerged as a promising class of nanomaterials due to their unique optical, electrical, and catalytic properties, positioning them as key players in electrocatalytic applications. This review provides a comprehensive and up-to-date analysis of CQDs, focusing on their electrocatalytic behavior in critical reactions such as the oxygen evolution reaction (OER), hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), bifunctional catalysis and liquid fuel electrooxidation. Distinct from prior studies, this study highlights recent innovations in CQD synthesis, including heteroatom doping and defect engineering, and explores their structural properties-like absorbance, photoluminescence, and electroluminescence-that enhance catalytic performance. We elucidate the electrocatalytic mechanisms (e.g., reactant adsorption, electron transfer, and intermediate stabilization) and address challenges such as low conductivity and scalability, proposing advanced strategies like hybridization with transition metals. Additionally, this review uniquely emphasizes the potential of CQDs in bifunctional catalysis and environmental applications, offering fresh insights into their role in advancing sustainable energy technologies.

Co-gasification of E-waste with sewage sludge for hydrogen production

The increasing accumulation of electronic waste (E-waste) and sewage sludge poses significant environmental and waste management challenges. This work taps on two non-conventional waste streams that have grown tremendously in the last decades, namely, E-waste (in the form of printed circuit boards (PCB)) and sewage sludge. We simulated entrained flow gasifier technology at 1250 °C and 30 bars of various mixture ratios of PCB and sludge (e.g., 40%, 60%, and 75% PCB with 60%, 40%, and 25% sludge) to produce valuable syngas. The primary objective is to optimize hydrogen production while addressing the limited research on E-waste gasification, particularly its synergistic interactions with sewage sludge. The work consists of studying the proximate, ultimate, and calorific analyses of these mixtures and FT-IR analysis to identify functional groups such as hydroxyls and carbonyls. Then, the XRD analysis to reveal the mix of crystalline and amorphous phases supporting diverse properties that enhances the gasification efficiency along with SEM imaging to show the distinct surface characteristics, with varied porosity that improves reaction dynamics. The equilibrium-based gasification based on energy and mass conservation principles is conducted first at sweeping temperatures up to 1,250 °C revealing the appropriate mixture fractions of 40% PCB and 60% sludge that produces the highest hydrogen moles fraction of 0.430 and cold gasification efficiency (CGE) of 49.86%. A high-fidelity 3D reactive flow then developed that integrates the effects of turbulence, heat transfer, and particle dynamics, offering a more realistic evaluation of the entrained flow gasification process, with the 40% PCB mixture yielding 0.03 mol of H2 at the gasifier's exit. Results showed lower and more reasonable syngas molar fraction and CGE (H2 = 0.03, CO2 = 0.12, and CGE = 17.50) than the equilibrium-based model. The findings suggest that increasing the mass percentage of PCB reduces CO and H2 concentrations due to lower volatile matter and higher oxygen content. This study highlights the potential of co-gasification of E-waste with sewage sludge as a viable solution and dually managing E-waste and sludges that are heavily increased in the MENA region for the production in hydrogen/syngas energy source.

Novel intelligent naked-eye food packaging pH-sensitive and fluorescent sulfur, nitrogen-carbon dots biosensors for tomato spoilage detection including DFT and molecular docking characterization

Tomatoes are susceptible to microbial spoilage, leading to significant economic losses. This study introduces a novel approach to monitor tomato spoilage. Carboxymethyl cellulose (CMC) films incorporated with sulfur and nitrogen-doped carbon dots (SN-CDs) were developed as pH-sensitive colorimetric sensors for tomatoes. The SN-CDs, derived from red onion peel waste (OPW), exhibited excellent fluorescence properties and antimicrobial activity XPS analysis confirmed the successful synthesis of SN-CDs with incorporated N and S. The incorporation of OPW significantly reduced the Young's modulus of the CMC hydrogel film, likely due to structural disruptions and increased free volume within the film. The color of the prepared colorimetric sensors was changed after tomato spoilage which means the effectiveness of these films in the tomato spoilage detection by naked eye. It exhibited pH-sensitivity because of the presence of flavonoids due to structural changes, including protonation and deprotonation. This pH sensitivity allows for visual indication of pH changes, as demonstrated by the CMC-SN-CDs3 film, which turns yellow in acidic conditions and red in alkaline conditions. The CMC-SN-CDs films displayed a distinct color change in response to pH variations, enabling visual detection of tomato spoilage. DFT calculations and molecular docking studies support the findings.

Application of electrospun N-doped carbon dots loaded cellulose acetate membranes as cationic dyes adsorbent

This work aims to apply carbon quantum dots (CQDs) from agriculture cellulosic waste (agro wastes), produced via an economically and eco-friendly single-step method, to be used into cellulose acetate composite microfibrous membranes as an innovative solution specifically designed to adsorb methylene blue (MB) and other cationic dyes that are present in various water effluents. Batch adsorption tests were conducted, with variations in contact time (1-24 h), initial MB concentration (25-300 ppm), and adsorbent doses (1-20 g/L). The maximum adsorption capacity of the membrane was 198 mg/g with an initial concentration of 300 ppm at 298 K. Thermodynamic parameters showed that the process is endothermic. Equilibrium experimental data for MB adsorption onto electrospun adsorbent were fitted using different isothermal models, with the Freundlich model showing the best fit. The pseudo-second-order model accurately described the kinetic data with high reliability (R2 > 0.99), and the calculated adsorption capacity was very close to the experimental data. N-CQDs loaded membranes were also tested for removing methyl violet and rhodamine B, demonstrating remarkably high dye removal efficiency. The underlying adsorption mechanism was also reported. Finally, it is worth mentioning that composite adsorbents can be efficiently applied to actual industrial cases because of the possibility of reusing them, opening the route to the fabrication of novel and highly performant adsorbents. These findings underscore N-CQDs' effectiveness in enhancing pollutant removal efficiency from wastewater, highlighting their environmental benefits and promoting a more sustainable approach to water treatment. Therefore, the prepared adsorbent, showing excellent adsorption performance, places them among adsorbents for practical applications in wastewater purification.

Tracking of the conversion and transformation pathways of dissolved organic matter in sludge hydrothermal liquids during Cr(VI) reduction using FT-ICR MS

In this study, the remediation effects of two types of sludge (ferric-based flocculant and non-ferric-based flocculant) on Cr(VI)-polluted wastewater were evaluated to clarify the key components in sludge hydrothermal solutions responsible for reducing Cr(VI) and understand the underlying molecular-level transformation mechanisms. The results revealed that the primary reactions during the hydrothermal processes were deamination and decarboxylation reactions. Correlation analysis highlighted proteins, reducing sugars, amino groups, and phenolic hydroxyl groups as the major contributors. In-depth analysis of the transformation process of functional groups within dissolved organic matter (DOM) and synergistic redox process between Cr(VI) and DOM in hydrothermal solutions demonstrated that phenolic hydroxyl and amino groups gradually underwent oxidation during reduction of Cr(VI) by DOM, forming aldehyde and carboxyl groups, among the others. Time-dependent density functional theory calculations revealed notable shift of reducing functional groups from ground state to excited state following iron complexation, ultimately facilitating reduction reaction. Subsequent investigations, including soil column leaching and seed germination rate tests, indicated that synergistic redox interaction between Cr(VI) and DOM significantly reduced waterborne heavy metal and toxic organic pollution. These findings carry substantial implications for sludge treatment and remediation of heavy metal pollution in wastewater, offering valuable insights into effective environmental remediation strategies.

Microwave-Prepared Quantum Dots and Their Potential Applications as Adsorbents and Chemosensors

A combination of different eco-friendly materials prepared promising fluorescent quantum dots (QDs) through the one-step process using the microwave heating of urea with cellulose, chitosan, and biochar. Characterizations of the prepared QDs, including the investigation of their structure by infrared spectroscopy, Raman analysis, X-ray diffraction, thermal gravimetric analysis, morphology, and optical properties, were performed. The results showed that QDs possess a small size, high UV absorption, and excitation wavelength-dependent fluorescence. The prepared QDs were also tested for metal ions removal from aqueous solutions. The adsorption at different contact times was investigated to optimize the adsorption efficiency of the prepared QDs. All QDs were found to be an ideal sorbent for Cr(II), Cu(II), Mn(II), and Pb(II). From the data, Cr(II) was more highly adsorbed than other metal ions. The results of the kinetic investigation showed that the pseudo-second-order kinetic model fit the adsorption process effectively. In addition, the fluorescence spectra of QDs were changed after the adsorption of metal ions; hence, the prepared QDs could be utilized in environmental sectors such as wastewater pollution detection, adsorption, and chemical sensing applications.

Thermal Evaluation of Silica-Based Insulated Magnet Wires from the Sol-Gel Process

The conventional enameling process used in the fabrication of magnet wires requires harmful processes and products. The target of the industry in the actual context of electrification is to increase the electrical machines' efficiency. Indeed, the electrical insulation systems (EIS) of an electrical machine undergo various environmental constraints that can shorten their lifespans. Consequently, aspects of the insulation need to be improved, such as its thermal resistance. One of the challenges is to implement sustainable technology without losing performance. This work consists of the thermal performance evaluation of new magnet wires insulated by three types of composites of silica-based solution from the Sol-gel process and amorphous polyamide-imide (PAI). These composite coats are overcoated by an extruded thermoplastic resin with and without fillers. Different types of insulation are tested and compared to determine the better configuration. Thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) analysis, scanning electron microscopy (SEM) analysis, curing characteristics by tangent delta curve, and thermal-aging tests at three temperatures were carried out on the different EIS systems. Dielectric measurements were made between thermal-aging cycles. Their basic mechanical, electrical, and thermal characteristics are promising: the cut-through temperature is situated above 430 °C, their breakdown voltage values are between 5 kV and 9 kV (grade 3), and a good adhesion (overcoming more than 140 turns on a peel test). The thermal-aging results have been consistent with the TGA analysis results. The thermal index following the IEC standards was estimated for the selected EIS, which would have the main basic characteristics of a magnet wire of 200 class; moreover, it would be a greener enameled wire compared to the conventional one.

Investigations on the preparation of ceramsite from petrochemical excess sludge

Petrochemical excess sludge, as hazardous solid waste, poses a great threat to the environment and is difficult to dispose of in an economic and environmentally friendly way. A new alternative of using the petrochemical excess sludge to prepare ceramsite is proposed. The relationship between the sintering behavior of dried excess sludge, including the composition, temperature, fluxing agent, and pore-forming agent addition, and the properties of ceramsite is investigated. The properties of ceramsite are primarily affected by the sintering temperature and the addition of a fluxing agent. Ceramsite with a sintering-expanded surface is prepared. Also, its water absorption is quite low, indicating an improvement in densification due to sintering. Moreover, the leaching toxicity of the heavy metals in the dried excess sludge and prepared ceramsite is also investigated. It reveals the feasibility of ceramsite preparation by sintering petrochemical excess sludge.