The continuous decrease in the availability of fossil resources, along with an evident energy crisis, and the growing environmental impact due to their use, has pushed scientific research towards the ...development of innovative strategies and green routes for the use of renewable resources, not only in the field of energy production but also for the production of novel advanced materials and platform molecules for the modern chemical industry. A new class of promising carbon nanomaterials, especially graphene quantum dots (GQDs), due to their exceptional chemical-physical features, have been studied in many applications, such as biosensors, solar cells, electrochemical devices, optical sensors, and rechargeable batteries. Therefore, this review focuses on recent results in GQDs synthesis by green, easy, and low-cost synthetic processes from eco-friendly raw materials and biomass-waste. Significant advances in recent years on promising recent applications in the field of electrochemical sensors, have also been discussed. Finally, challenges and future perspectives with possible research directions in the topic are briefly summarized.
A novel bidentate Schiff base (L) is here proposed for the detection of Zn ions in water. The structure of the synthesized Schiff base L was characterized by FT-IR,
H NMR and
C NMR. Optical ...characteristics were addressed by UV-Visible spectroscopy and Photoluminescence (PL) measurements. PL demonstrated that L displays a "turn-off" type fluorescence quenching in the presence of Zn
ion in aqueous solution, indicating its ability to preferentially coordinate this ion. Based on these findings, an L-M (where M is a suitable membrane) modified screen-printed carbon electrode (SPCE) was developed to evaluate the electrochemical behavior of the Schiff base (L) with the final objective of undertaking the electroanalytical determination of Zn ions in water. Using various electrochemical techniques, the modified L-M/SPCE sensor demonstrates high sensitivity and selectivity to Zn ions over some common interferents ions, such as Ca
, Mg
, K
, Ni
and Cd
. The potentiometric response of the L-M/SPCE sensor to Zn ions was found to be linear over a relatively wide concentration range from 1 μM to 100 mM.
Carbon dots (CDs) samples were synthesized from orange peel waste (OPW) via a simple and eco‐friendly hydrothermal carbonization (HTC) and electrochemical (EC) bottom‐up synthesis integrated ...approach. The comprehensive chemical‐physical characterization of CDs samples, carried out by various techniques such as TEM, EDX, XRD, FT‐IR, underlined their morphological and microstructural features. The CDs exhibited attractive electrochemical properties, and thus an electrochemical sensor by modifying a screen printed carbon electrode (CDs/SPCE) for the detection of nitrobenzene (NB) in water was developed. Electroanalytical performances of CDs/SPCE sensor using differential pulse voltammetry (DPV) demonstrated its high sensitivity (9.36 μA μM−1 cm−2) towards NB in a wide linear dynamic range (0.1–2000 μM) and a low limit of detection (LOD=13 nM). The electrochemical sensor also shown high selectivity, long‐term stability, and repeatability. This paper might open the way to a new synergistic HTC‐EC approach for the synthesis of CDs from waste biomass material and their advanced application in highly efficient electrochemical sensors.
Not just waste: An integrated approach based on linking thermal and electrochemical technologies is investigated for the valorisation of agro‐industrial waste. The obtained carbon dots (CDs) are certain of high scientific value and may add more value to industrial citrus waste. The CDs exhibited interesting physicochemical and optical properties, allowing their use as a voltammetric sensor.
In this study, a simple and green protocol to obtain hydrochar and high-added value products, mainly 5-hydroxymethylfurfural (5-HMF), furfural (FU), levulinic acid (LA) and alkyl levulinates, by ...using the hydrothermal carbonization (HTC) of orange peel waste (OPW) is presented. Process variables, such as reaction temperature (180–300 °C), reaction time (60–300 min), biomass:water ratio and initial pH were investigated in order to find the optimum conditions that maximize both the yields of solid hydrochar and 5-HMF and levulinates in the bio-oil. Data obtained evidence that the highest yield of hydrochar is obtained at a 210 °C reaction temperature, 180 min residence time, 6/1 w/w orange peel waste to water ratio and a 3.6 initial pH. The bio-products distribution strongly depends on the applied reaction conditions. Overall, 180 °C was found to be the best reaction temperature that maximizes the production of furfural and 5-HMF in the presence of pure water as a reaction medium.
In the present work, a study was carried out with the aim of enhancing the performance of electrochemical biosensors based on Co3O4:Fe2O3 heterojunctions. Specifically, the redox behavior of ...screen–printed carbon electrodes (SPCEs) modified with Co3O4:Fe2O3 (0.5 wt%:x wt%) nanocomposites, where x ranged from 0.1 to 0.5 wt%, was examined in detail. The hybrid nanocomposites were synthesized using the sol-gel auto-combustion method. Several characterization methods were performed to investigate the morphology, microstructure, and surface area of the pure Co3O4, pure Fe2O3, and the synthesized Co3O4:Fe2O3 nanocomposites. Using cyclic voltammetry (CV) tests, the electrochemical behavior of the modified electrodes toward the dopamine (DA) molecules was investigated. The modified Co3O4:Fe2O3, (0.5 wt%, x = 0.4 wt%)/SPCE resulted in a sensor with the best electrochemical performance toward DA. A high linear relationship between DA concentrations and the faradic current variation (ipa (μA) = 0.0736 + 0.1031 CDA (μA) and R2 = 0.99) was found in the range of 10–100 μM. The sensitivity value was computed to be 0.604 µA µM−1cm−2 and the limit of detection (LOD) 0.24 µM. Based on the characterization and electrochemical results, it can be suggested that the formation of Co3O4:Fe2O3 heterostructures provides a large specific surface area, an increased number of electroactive sites at the metal oxide interface and a p–n heterojunction, thus ensuring a remarkable enhancement in the electrochemical response towards DA.
Seaweeds are considered a biomass for third-generation biofuel, and hydrothermal carbonization (HTC) is a valuable process for efficiently disposing of the excess of macroalgae biomass for conversion ...into multiple value-added products. However, the HTC process produces a liquid phase to be disposed of. The present study aims to investigate the effects of seed-priming treatment with three HTC-discarded liquid phases (namely AHL
, AHL
, and AHL
), obtained from different experimental procedures, on seed germination and plant growth and productivity of
L. To disentangle the osmotic effects from the use of AHL, isotonic solutions of polyethylene glycol (PEG) 6000 have also been tested. Seed germination was not affected by AHL seed-priming treatment. In contrast, PEG-treated samples showed significantly lower seed germination success. AHL-treated samples showed changes in plant biomass: higher shoot biomass was recorded especially in AHL
samples. Conversely, AHL
and AHL
samples showed higher root biomass. The higher plant biomass values recorded in AHL-treated samples were the consequence of higher values of photosynthesis rate and water use efficiency, which, in turn, were related to higher stomatal density. Recorded data strongly support the hypothesis of the AHL solution reuse in agriculture in the framework of resource management and circular green economy.
•Waste-to-fuel strategy combining orange peel valorization and CO2 conversion.•Metal-free orange peel waste–derived carbon nanodots were synthesized.•Highly active and selective system in CO2 ...photoreduction to methanol.•Maximum methanol production rate of 416.6 µmolMeOH.gcat-1.h−1.•Highly stable methanol rate of 12.9 µmolMeOH.gcat-1.h−1 after 72 h.
Addressing the major challenge of global warming by implementing a circular carbon cycle involving CO2 conversion is currently an urgent priority for a more sustainable future. The design of efficient, stable, cheap and eco-friendly systems for such purpose is a remarkable challenge. This study reports an unprecedented metal-free, co-catalyst-free orange peel waste–derived carbon nanodot highly active and selective system for the photoreduction of CO2 into methanol. The waste-derived photocatalyst exhibited a maximum methanol production rate of 416.6 µmolMeOH.gcat-1.h−1 and a highly stable methanol production rate of 12.9 µmolMeOH.gcat-1.h−1 after 72 h. This work proposes a successful waste-to-fuel strategy that combines the valorization of orange peel waste and CO2 conversion for the synthesis of green methanol.
Carbon dots (CDs), a class of novel zero-dimensional nanomaterials, have recently emerged as excellent candidates for versatile applications in several fields due to their superior properties such as ...excellent photostability and biocompatibility, low cytotoxicity, small size, fluorescence, and ease of surface modification. The use of a more environmentally friendly source to produce high-quality CDs remains a crucial issue to be addressed. “Green” CDs have attracted a lot of attention recently and renewable biomass, especially waste biomass, is a good choice for large-scale CDs synthesis because it not only promotes outstanding properties, has excellent properties but also provides a green solution to balance waste management goals with those of the circular economy. Here, we highlight recent advances in green synthesis and formation mechanism of CDs from biomass, focusing on innovative one-pot hydrothermal and microwave processes.
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Palladium nanoparticles find extensive applications in catalysis in both homogeneously and heterogeneously catalyzed processes. Supporting metal nanoparticles enhances their stability as compared to ...their unsupported counterparts. The role of catalytic support is increasingly recognized as crucial in determining the behaviour of these materials. However, controlling the deposition and anchoring of palladium nanoparticles remains a significant challenge. This contribution discusses the preparation of straight lines of palladium particles on zinc oxide by wet impregnation. This phenomenon is attributed to the highly stepped morphology of the employed ZnO that created steric anchoring sites to stabilize the metal particles. Palladium-based catalysts were evaluated for the valuable Suzuki-Miyaura cross-coupling reaction. The dispersed Pd/ZnO catalyst achieved a conversion rate of 86% with 100% selectivity, remarkably superior to that of the Pd/Al
2
O
3
and Pd/TiO
2
counterparts.
Precise placement of Palladium (Pd) nanoparticles onto ZnO surfaces, resulting in improved performance in Suzuki-Miyaura cross-coupling processes due to accurate catalyst dispersion.
The total annual production of agricultural biomass such as wood, corn cobs, leaves, and citrus peels, is estimated at 956 million tons (Mt). Since crop residues are by-products of agricultural ...production, crop residue collection does not compete with food crops for acreage and therefore, it does not negatively impact food prices. Moreover, it has the advantage of reducing the amount of waste, the disposal of which often becomes a serious problem despite natural sources. Biomass conversion becomes a very valid alternative to diversify energy sources and reduce global warming. Thermochemical treatment of biomass is a promising way to convert biomass into bio-oil, biochar, and gas. In recent years, interest in the conversion of plant biomass into biochar has increased because this carbonaceous material has interesting properties that guarantee applications in wastewater treatment, soil improvement, solid fuels, and energy. The processes performed to convert biomass into biochar are different and the most used are thermochemical processes: pyrolysis, torrefaction, hydrothermal treatment, and gasification. The studies of the thermokinetic parameters that control these processes are carried out using different methods that provide the necessary information for the applicability of the processes on an industrial scale. One of the objectives of the present review is to compare kinetic models in order to clarify the role of the conversion process and the effects of the process parameters on the final product. A comprehensive investigation of the thermokinetic parameters controlling the conversion of crop residues to biochar was conducted. The mathematical description of kinetic processes is usually performed using the Arrhenius equation and its derivatives to obtain the activation energies (
E
a
), the pre-exponential parameter, and the process mechanisms. While isothermal processes can be described using the model fitting method, isoconversional processes can be studied using both the model fitting method and model-free methods. The high complexity and diversity of the reactions involved could lead to the use of approximations. In this paper, an overview of the kinetic parameters determined for biochar production processes and the model used to determine them is given.
Thermokinetics of Biochar production.
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