Presence Of Carbon Quantum Dots Research Articles

Design and optimization of a Cr(VI)-Selective Electrode based on a polymeric ß-cyclodextrin membrane modified with sulfur donor groups

This work presents the design and optimization of a new Cr(VI)-selective electrode. The new sensor is based on modifying a glassy carbon electrode with carbon quantum dots, ß-cyclodextrin, and carbon disulfide. The carbon quantum dots aided the electrical properties of the glassy carbon by improving charge transfer; the electropolymerization of ß-cyclodextrin resulted in a polymeric membrane that functions as a recognition element when modified by adding sulfur donor groups to its structure. Modifying the membrane with sulfur atoms gave the sensor excellent selectivity toward Cr(VI) ions. The electrode synthesis was optimized using a 23 factorial design; the factors studied were pH, the number of cycles in the electropolymerization, and the presence or absence of carbon nanoparticles. Eight different electrodes were constructed, and their potentiometric response to different concentrations of Cr(VI) was evaluated for all of them. The analysis of variance of the experimental design found no significant effect of any factor on the response. However, it suggests a strong interaction between the three factors studied. The sensor that presented the best analytical parameters was synthesized at pH 5 and 50 consecutive cycles in the presence of carbon quantum dots. This new electrode, with its response times of 40 s at different concentrations of the metal ion, exhibiting a slope of (66.0 ± 2.1) mV decade−1 and a detection limit of (5.2 ± 0.1)x10−7 mol L−1, can be used at pH between 0 and 3 without the effect of hydronium ions. The proposed electrode has good reproducibility and excellent selectivity against various metal ions and has significant advantages over other analysis methods. Its cost, ease of construction, easy handling, ease of operation, ease of storage and transportation, as well as good performance, short response time, and high selectivity make this electrode a valuable tool for easy, fast, and reliable monitoring of Cr(VI) in water samples, contributing to the safety and health of our environment.

Investigating the presence of carbon quantum dots in the inhalable aerosol from electronic cigarettes

Investigating the presence of carbon quantum dots in the inhalable aerosol from electronic cigarettes

Microstructure and Water Vapor Barrier Performance of Organic‐Bridged Polysilsesquioxane/Carbon Quantum Dots Composite Coatings

Developing siloxane‐based coatings with excellent water vapor barrier ability is of great importance due to their wide applications for various optical‐related fields. To improve the water vapor barrier ability of polysilsesquioxane coatings, this research proposes a strategy of introducing carbon quantum dots (CQDs) into organic‐bridged polysilsesquioxane coatings to enhance their water vapor barrier property. The CQDs are prepared by the pyrolysis of citric acid and then the composite coatings are prepared by thioether‐ester‐bridged silsesquioxane precursor in situ hydrolysis and condensation in the presence of CQDs. The experimental results show that the CQDs disperse well in the polysilsesquioxane matrix which is conducive to provide long diffusion pathway of water vapor molecules and also introduce individual “bubble pores” into the composite coatings. Thus‐obtained composite coatings not only show fivefold enhancement in water vapor barrier ability compared to the polysilsesquioxane coating without CQDs, but also perform good light transparence and good UV radiation‐resistant property, which would satisfy the requirements of optical‐related moisture‐resistant application fields.

A solar flow photo-reactor for antibiotic removal from aquaculture effluents using TiO2/carbon quantum dots

Effluents contaminated with antibiotics must be treated before reuse or even discharge into the aquatic environment, avoiding the increase of antimicrobial resistance (AMR) – a major public health problem of the 21st century. Little is known regarding the natural solar photodegradation of antibiotics in tubular reactors operated under flow mode and even less concerning the application of photocatalysts. The use of photocatalysts is considered a promising strategy for a sustainable solar-driven removal of antibiotics from effluents. In this work, the photodegradation of two antibiotics widely used in aquaculture, namely, sulfadiazine (SDZ) and oxolinic acid (OXA), was investigated under solar flow mode in the absence and presence of carbon quantum dots (CQDs) coupled with titanium dioxide (TiO2) (4% (w/w)). The obtained results showed that TiO2/CQDs (4% (w/w)) enhanced the photodegradation of both antibiotics, which is highly beneficial for their application in the treatment of aquaculture effluents. The accumulated UV energy needed for SDZ removal using the photocatalyst was less than 4 kJ L−1 in both simulated freshwater (phosphate buffer solution (PBS)) and simulated brackish water (sea salt solution (SSS)), while for OXA less than 5 kJ L−1 and around 15 kJ L−1 were needed for removal in PBS and in SSS, respectively. Moreover, results demonstrated that the proposed photocatalytic treatment was also efficient in the elimination of OXA and SDZ antibacterial activity, either in PBS or SSS. Therefore, photocatalysis under flow mode using TiO2/CQDs constitutes a promising and sustainable treatment for antibiotics’ efficient removal from aquaculture effluents.

Ball mill-hydrothermal method for one-step synthesis of zinc oxide/carbon quantum dot (ZnO-CQD) nanocomposites as photocatalyst for degradation of organic pollutants

In this work, we report a cost-effective, green, one-step, and new method without any extra materials to prepare ZnO/CQD photocatalyst. Hence, ZnO nanoparticles and zinc oxide/carbon quantum dot (Z-CQD) nanocomposites were synthesized using zinc salt, KOH, and sucrose through the new green ball mill-hydrothermal method. The prepared nanomaterials were characterized by FT-IR, TEM, XRD, FE-SEM, TGA, and UV–Vis absorption. The analysis of the TGA result shows the presence of around 6 wt% of CQD in Z-CQD nanocomposite. The presence of CQD in ZnO nanoparticles decreased the bandgap. The photocatalytic performance of ZnO and Z-CQD were compared by evaluating the degradation of phenazopyridine (PhP), a drug pollutant, and rhodamine B (RhB), an organic dye pollutant, under UV light. The results showed that the degradation rate of RhB is higher than that of PhP. In addition, in the case of RhB, the degradation rate by Z-CQD is higher than that of pure ZnO. Therefore, the presence of carbon quantum dots showed a positive effect on the rate of photocatalytic degradation.

Selective and Rapid Optical Detection of Citalopram Using a Fluorescent Probe Based on Carbon Quantum Dots Embedded in Silica Molecularly Imprinted Polymer.

In this study, a citalopram optical nano-sensor was developed. Citalopram is a well-known antidepressant drug that reduces the reuptake of serotonin in neurons as a result, serotonin neurotransmission, the primary response to antidepressant treatments, increases in many parts of the brain. This study introduces a carbon quantum dots (CQDs)-based optical nanosensor for rapid detection of citalopram. This fluorescent nanosensor was made through the polymerization of tetraethyl orthosilicate in the presence of CQDs as the fluorescent materials and citalopram as the template molecule. Following the polymerization, the templated molecules were washed and removed from the structure, and the matrix of the polymer was left with some cavities that resembled citalopram in terms of size and shape. The final structure which is used as a chemical nanosensor, is named carbon quantum dots embedded silica molecularly imprinted polymer (CQDs-SMIP). The materials used in designing nano-sensors were characterized using FTIR, UV/Vis, and fluorescence spectroscopy, as well as high-resolution transmission electron microscopy (HR-TEM), and field emission scanning electron microscopy (FESEM). CQDs-SMIP showed a strong fluorescence emission at 420nm in the absence of the template molecule. The fluorescence intensity of the nanosensor decreased in the presence of citalopram. The correlation between the extent of the fluorescence quenching and the concentration of citalopram provided the nano-sensor signal. The nano-sensor was used to measure citalopram in complex matrices such as human plasma and urine samples with remarkable selectivity and sensitivity. The detection limit of 10.3µg.L-1 over a linear range of 100 to 700µg.L-1, and RSD of 3.15% was obtained. This nano-sensor was applied to analyze of citalopram in plasma and human urine samples with remarkable results.

Carbon quantum dots as immune modulatory therapy in a Sjögren's syndrome mouse model.

The objective of the study was to evaluate the therapeutic effects of carbon quantum dots (CQDs) in immunomodulation on non-obese diabetic (NOD) mice, as the model for Sjögren's syndrome (SS). Carbon quantum dots were generated from Setaria viridis via a hydrothermal process. Their toxic effects were tested by cell viability and blood chemistry analysis, meanwhile therapeutic effects were investigated in NOD mice in the aspects of saliva flow, histology, and immune cell distribution. Carbon quantum dots, with rich surface chemistry and unique optical properties, showed non-cytotoxicity in vitro or no damage in vivo. Intravenously applied CQDs alleviated inflammation in the submandibular glands in NOD mice after 6-week treatments. The inflammatory area index and focus score were significantly decreased in CQD-treated mice. Besides, the levels of anti-SSA and anti-SSB were decreased in the presence of CQDs. The stimulated saliva flow rates and weight of submandibular glands were significantly increased in CQD-treated mice by reducing the apoptosis of cells. The CD3+ and CD4+ T cells distributed around the ducts of submandibular glands were significantly decreased, while the percentage of Foxp3+ cells was higher in CQD-treated mice than that in the control group. Our findings suggest that CQDs may ameliorate the dysregulated immune processes in NOD mice.

Impact of carbon quantum dots on self-assembly and dielectric relaxation modes of a room temperature tri-component fluorinated antiferroelectric liquid crystal mixture.

We investigated the impact of carbon quantum dots (CQDs) of sizes ∼2-5 nm in a room temperature tri-component fluorinated antiferroelectric liquid crystal (AFLC) mixture. The synthesised CQDs have been characterised by high-resolution transmission electron microscopy and X-ray diffraction spectroscopy. An increase in the transition temperature and enthalpy to the isotropic liquid phase indicates stabilization of the AFLC mixture in the presence of CQDs. The dielectric studies have been carried out in the frequency range of 1 Hz-40 MHz under the planar anchoring conditions of the molecules. An appreciable increase in the permittivity, dielectric strength, and conductivity has been observed owing to the existence of sp2/sp3 hybridization in the CQDs which form a strong coupling and develop a dipolar ordering in the systems. Various relaxation frequencies were increased with the incarceration of CQDs in the AFLC mixture. Overall, the different studies suggest that the doped CQDs are very well settled in between the host molecules without disturbing the molecular ordering of the hosts. Such results are encouraging and reveal the potential applicability of the CQD doped systems to produce highly efficient tuneable optical devices and other multifaceted applications.

Carbon quantum dots and chitosan-based heterogeneous silver catalyst for reduction of nitroaromatic compounds.

Chitosan plays a crucial role in catalysis, environmental remediation, and sustainable chemistry as a renewable and cationic polysaccharide. Chitosan-based metal catalysts are used in a broad range of chemical transformations. In the study, carbon quantum dots (CQDs) were derived from Momordica charantia fruits by microwave irradiation following a green chemistry approach. Three catalysts were designed: Ag(0)-chitosan, Ag(0)-chitosan-M. charantia fruit powder, and Ag(0)-chitosan-CQDs. The catalyst supports were prepared by stabilizing CQDs or M. charantia powder within the polymeric matrix of chitosan beads. Metallic silver particles were anchored onto glutaraldehyde cross-linked chitosan beads from the aqueous solution of silver nitrate. The heterogeneous silver catalysts were used to reduce toxic nitroaromatics (4-nitrophenol, 2-nitroaniline, 1,2-diamino-4-nitrobenzene, 2,4-dinitrophenol). The regeneration of catalysts was also covered. The reused catalysts retained their catalytic activities after ten cycles. The study suggested that presence of CQDs or M. charantia powder could improve the efficiency of the chitosan-based metallic silver catalysts.

Role of carbon quantum dots in a strategic approach to prepare pristine Zn2SnO4 and enhance photocatalytic activity under direct sunlight

In the present work, carbon quantum dots (CQDs) are used in a strategic approach to obtain pristine mesoporous Zn 2 SnO 4 (ZTO) and enhanced photodegradation of methylene blue (MB) dye. The Zn 2 SnO 4 /carbon quantum dots (ZTO/C) was hydrothermally prepared using mineralizer, Na 2 CO 3 and quantified amount of sugarcane juice. The mesoporous nature and high surface area of ZTO and ZTO/C was revealed from Brunauer, Emmett and Teller (BET). The close overlapping of CQD with ZTO was evident from the HRTEM and Raman spectra. The MB dye degradation study employing ZTO and ZTO/C catalyst under direct sunlight irradiation showed 84 % and 95 % degradation in 150 min respectively. The presence of CQDs in ZTO/C nanocomposites enhanced the transportation of photoinduced electrons at the interface between ZTO and CQDs, whereas holes stayed in the valence band of ZTO, suppressing the recombination of photogenerated charge carriers during photocatalysis. This study reveals that ZTO/C as a possible candidate for sunlight-driven photocatalysis and environmental remediation. • Synthesis of pristine mesoporous Zn 2 SnO 4 (ZTO) and Zn 2 SnO 4 /carbon quantum dots (ZTO/C) in a strategic method using CQDs • Green synthesis of Carbon quantum dots using sugar cane juice. • High photocatalytic degradation efficiency of 95 % using (ZTO/C) nanocomposite towards methylene blue (MB) dye.

Effect of synthesized carbon quantum dots on the photocatalytic properties of ZnO

ABSTRACT. In this work, synthesized carbon quantum dots (CQDs) and zinc oxide nanoparticles (ZnO NPs) are used to form ZnO/CQDs nanocomposite. The characterization of this nanocomposite using X-ray diffraction (XRD) indicates that ZnO NPs and ZnO/CQDs nanocomposite have the same profile, suggesting that the presence of CQDs does not impinge the crystal structure of ZnO in ZnO/CQDs nanocomposite. Besides, an analysis performed with scanning electron microscopy (SEM) displays plate-like nanostructure with an average thickness of about 22 nm and 25 nm for ZnO NPs and ZnO/CQDs, respectively. Furthermore, the reflectance study in the visible range shows a reduction of sunlight reflection intensity of ZnO/CQDs compared with the reflection intensity of ZnO NPs. In addition, the photocatalytic studies indicate that the rate of photocatalytic degradation of methylene blue (MB) of ZnO/CQDs nanocomposites is higher than that of ZnO NPs. Indeed, in optimized conditions, the photocatalytic activity can reach 100% within 45 min of sunlight exposure for the degradation of 7.5 mg/L MB using ZnO/CQDs while it takes 90 min using ZnO NPs under the same conditions. These fascinating results is attributed to the reduction of the reflective properties of ZnO/CQDs.
 
 KEY WORDS: Fluorescent carbon quantum dots (CQDs), Photocatalytic degradation of methylene blue, Sunlight reflectance property, Synthesis of ZnO nanoparticles
 Bull. Chem. Soc. Ethiop. 2023, 37(2), 463-476. 
 DOI: https://dx.doi.org/10.4314/bcse.v37i2.15

Inhibitory activity of carbon quantum dots against Phytophthora infestans and fungal plant pathogens and their effect on dsRNA-induced gene silencing

Carbon quantum dots (CQDs) have many potential applications due to their cell-penetrating ability, biocompatibility and tunable properties. Among a variety of characteristics, the inhibition of bacteria by CQDs is often reported. However, the effect on other microorganisms, such as plant pathogenic fungi and oomycetes, is poorly studied. Here we monitored the growth of the oomycete plant pathogen Phytophthora infestans in the presence of CQDs, as well as of another three fungal plant pathogens, namely Botrytis cinerea, Alternaria alternata and Fusarium oxysporum. Moreover, the ability of CQDs to improve gene silencing caused by exogenous dsRNA in P. infestans was studied, and the toxicity of CQDs to human keratinocytes was evaluated. Our results indicate significant inhibitory activity of CQDs against P. infestans at relatively low concentrations. In a species-specific manner and to a lesser extent, the growth of the three fungal plant pathogens was also affected. We also found that the treatment of P. infestans with naked dsRNA in vitro did not trigger gene silencing. However, the mixture of CQDs with dsRNA increased RNAi efficiency, by causing a significant reduction of the transcript levels of the target gene in developing sporangia. Finally, no cytotoxicity of the CQDs, in the concentrations active against the plant pathogens, was found.

Carbon Quantum Dots Bridged TiO2/CdIn2S4 toward Photocatalytic Upgrading of Polycyclic Aromatic Hydrocarbons to Benzaldehyde.

Conversion of hazardous compounds to value-added chemicals using clean energy possesses massive industrial interest. This applies especially to the hazardous compounds that are frequently released in daily life. In this work, a S-scheme photocatalyst is optimized by rational loading of carbon quantum dots (CQDs) during the synthetic process. As a bridge, the presence of CQDs between TiO2 and CdIn2S4 improves the electron extraction from TiO2 and supports the charge transport in S-scheme. Thanks to this, the TiO2/CQDs/CdIn2S4 presents outstanding photoactivity in converting the polycyclic aromatic hydrocarbons (PAHs) released by cigarette to value-added benzaldehyde. The optimized photocatalyst performs 87.79% conversion rate and 72.76% selectivity in 1 h reaction under a simulated solar source, as confirmed by FT-IR and GC-MS. A combination of experiments and theoretical calculations are conducted to demonstrate the role of CQDs in TiO2/CQDs/CdIn2S4 toward photocatalysis.

A Versatile Synthetic Pathway for Producing Mesostructured Plasmonic Nanostructures.

Highly branched gold (Au) nanostructures with sharp tips are considered excellent substrates for surface-enhanced Raman scattering (SERS)-based sensing technologies. Here, a simple synthetic route for producing Au or Au-Ag bimetallic mesostructures with multiple sharpened tips in the presence of carbon quantum dots (CQDs) is presented. The morphologies of these mesostructured plasmonic nanoparticles (MSPNs) can be controlled by adjusting the concentration of CQDs, reaction temperatures, and seed particles. The optimal molar ratio for [HAuCl4 ]/[CQDs] is found to be ≈25. At this molar ratio, the diameters of MSPNs can be tuned from 80 to 200nm by changing the reaction temperature from 25 to 80 °C. In addition, it is found that hierarchical MSPNs consisting of multiple Au nanocrystals can be formed over the entire seed particle surface. Finally, the SERS activity of these MSPNs is examined through the detection of rhodamine 6G and methylene blue. Of the different mesostructures, the bimetallic MSPNs have the highest sensitivity with the ability to detect 10-7 m of rhodamine 6G and 10-6 m of methylene blue. The properties of these MSPN particles, made using a novel synthetic process, make them excellent candidates for SERS-based chemical sensing applications.

Urea-mediated synthesized carbon quantum dots to tune the electrochemical performance of polyaniline nanorods for supercapacitor device

A polyaniline (PANi)-carbon quantum dots (CQDs) nanocomposite material with CQDs made from a PEG (polyethylene glycol and NaOH) source was synthesized. This unique synthesis technique was developed to overcome the setbacks of the PEG method by using UG (urea and glycine). PANi was synthesized by chemical oxidation in the presence of CQDs, which were prepared according to the two above-mentioned methods. The sample was further characterized by morphological, optical, and electrochemical experiments. FE-SEM showed ridge-like morphology and UV-Vis studies revealed the presence of PANi and CQDs. HRTEM images gave details on the uniformly distributed polyaniline, which showed lengthy rod-like rough surfaces with interconnected tiny CQDs. The electrochemical results from CV and GCD studies indicated an enhancement of the specific capacitance for sample PCQ-2 (CQDs synthesized via the UG method as a source) compared to only PANi and PCQ-1 (CQDs prepared by the PEG method). The cyclic stability established was 84.5% retention from initial capacitance values over 3000 cycles. A two-electrode prototype device was also developed with the PCQ-2 sample and it achieved a reasonable capacitance of 161.3 mF/cm2 and demonstrated good retention stability over 5000 cycles. These results may be due to a variety of factors related to compositing CQDs (with urea and glycine as a source) with PANi.

Incorporation of carboxyl and amino functionalized carbon quantum dots in thin film membrane for nanofiltration

Fabrication of thin film nanocomposite membrane (TFN) with carbon quantum dots (CQDs) as nanofiller has gained a wide attention due to the promising properties of the CQDs to enhance the membrane permeability. Synthesis of CQDs and their functionalization with both carboxyl and amino groups are originated from rice husks as the precursor. Fourier-Transform Infrared Spectroscopy (FTIR) analysis shows that CQDs contain oxygen-containing groups that allow hydrogen bonding with water molecules. Zeta potential shows that the incorporation of CQDs produces highly negative charged membranes, while Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM) results indicate that the introduction of the nanoparticles alters the surface properties of the fabricated membranes. Photoluminescence (PL) analysis proves that CQDs are present in the polyamide (PA) layer which describes the unique characteristic of the CQDs. The presence of CQDs in TFN membranes assists in enhancing the performance of pristine thin film composite (TFC) membrane in both flux and salt rejection with values around 35 L/m2 h and 90%, respectively.

Enhanced photocatalytic hydrogen evolution using green carbon quantum dots modified 1-D CdS nanowires under visible light irradiation

Photoluminescent carbon quantum dots (CQD) have drawn intense attention due to its excellent optical properties, strong confinement effect, and good electrical conductivity. However, sustainable synthesis of CQD from green carbon sources and its application in water splitting has not been well explored. Herein, we synthesized CQD from orange peels and embedded them onto one-dimensional (1-D) cadmium sulfide (CdS) nanowires (average diameter 30 nm and length 2–4 µm) via a facile chemical adsorption method. The synthesized photocatalysts were thoroughly characterized using various spectroscopic, microscopic, diffraction, and photoelectrochemical techniques. The photocatalysts were tested for water-splitting reaction under visible light. The effect of mass fraction of CQD in CdS on water splitting performance has been investigated both in the presence and absence of sacrificial reagents. The reusability of the photocatalyst has also been tested. The optimal catalyst, 0.4CQD/CdS, exhibited the highest H2 production rate of 309 mmol g−1h−1 (apparent quantum yield of 32.6%) which is 1.5 times higher than that with bare CdS. The excellent photocatalytic performance of CQD/CdS was due to the existence of sulfur vacancies and the formation of cadmium oxide with effective charge transfer and separation. The higher photostability of CQD/CdS compared to that of CdS in three consecutive cycles can be attributed to suppression of photocorrosion of CdS in the presence of CQD.

Optical properties and zeta potential of carbon quantum dots (CQDs) dispersed nematic liquid crystal 4′- heptyl-4-biphenylcarbonitrile (7CB)

In this work, carbon quantum dots (CQDS) of three concentrations 0.1, 0.2 and 0.5 wt% have been dispersed in nematic liquid crystal 4′-Heptyl-4-biphenylcarbonitrile (7 CB). The results on the optical properties and zeta potential of pure and CQDs dispersed nematic 7CB have been reported. It has been observed that the dispersion of CQDs in host nematic matrix induces quenching of photoluminescence and reduces the Ultra-Violet-Visible (UV–Vis) absorbance of pure nematic at a lower wavelength. From the result of fluorescence decay profile, the fluorescence life time of pristine and dispersed nematic systems have been obtained. No remarkable changes in nematic lifetime in the presence of CQDs have been observed, which confirm that no energy is transferred from nematic to CQDs. Further, it has been found that due to dispersion of CQDs the numerical values of zeta potential are increased for the dispersed systems with 0.1 and 0.2 wt% concentrations of CQDs as compared to pure 7 CB. This result demonstrates that the study of zeta potential provides useful information on the stability and aggregation of the CQDs dispersed nematic systems.

Fluorometric determination of fipronil by integrating the advantages of molecularly imprinted silica and carbon quantum dots.

A fluorometric method is described for the determination of fipronil, a frequently-used insecticide. It exploits the blue fluorescence of carbon quantum dots (CQDs) and the selectivity of molecularly imprinted silica (MIS). The MIS was prepared via the sol-gel method by using fipronil as the template, 3-aminopropyltriethoxysilane as functional monomer, and tetraethoxysilane as cross-linker in the presence of CQDs. The blue fluorescence of the CQD@MIS, with excitation/emission peaks at 340/422nm, is quenched by fipronil. The assay works in the 0. 70 pM to 47μM fipronil concentration range, and the limit of detection is 19 pM. The method was successfully applied to the quantitation of fipronil in spiked eggs, milk, and tap water. Recoveries between 83.8 and 114.0% were achieved. The corresponding relative standard deviations (RSD) are less than 6.67%. Graphical abstractSchematic representation of a high sensitivite and selectivite fluorescence nanoprobe constructed by combining the excellent fluorescence property of carbon quantum dots and the predicted selectivity of molecularly imprinted silica. It was applied to analyze fipronil in egg, milk and tap water, respectively.

Influence of carbon quantum dots on the viscosity reduction of polyacrylamide solution

Viscosity is one of the key factors which influence the application of polyacrylamide (PAM) in enhanced oil recovery (EOR). In this study, we have demonstrated the viscosity reduction of PAM solution by using carbon quantum dots (CQDs) through rheological, spectroscopic and thermal analyses. The stability of PAM, CQDs, and PAM/CQDs composites, and the chemical interactions between PAM and CQDs were investigated. The addition of CQDs into PAM solution decreased its viscosity, demonstrating a phenomenon which contradicts the expression normally derived from the Einstein–Batchelor law for the viscosity of particle suspensions. Consequently, the elastic properties of PAM/CQDs composites were lower than those of the pure PAM solutions. Moreover, the presence of CQDs in the PAM increased its flow activation energy and decreased its yield point, leading to an increased sensitivity to both temperature and shear rate. The mechanism behind the reduced viscosity behaviour of PAM/CQDs composites appears to be the formation of free radicals and the elimination of ammonia molecules, leading to the deterioration of the polymer backbone.