Photocatalytic Degradation of Organic Dyes and Antimicrobial Activities by Polyaniline-Nitrogen-Doped Carbon Dot Nanocomposite

Chitosan/MgO NPs/CQDs bionanocomposite coating: Fabrication, characterization and determination of antimicrobial efficacy

The development of new polymer nanocomposites or antibacterial coatings is crucial in combating drug-resistant infections, particularly bacterial infections. In this study, a new chitosan polymer based nanocomposite reinforced with magnesium oxide nanopowders and carbon quantum dots was fabricated by sol-gel technique and coated on 316 L stainless steel. In order to gaining the optimal amount of components to achieve the maximum antibacterial properties, the effect of concentration of nanocomposite components on its antibacterial properties was investigated. Crystal structure, microstructure, elemental dispersion, size distribution, chemical composition and morphology of nanocomposite and coating were characterized with various analyses. The obtained results exhibited that the carbon quantum dot and magnesium oxide nanopowders were distributed uniformly and without agglomeration in the chitosan matrix and created a uniform coating. The antibacterial properties of the synthesized samples against Staphylococcus aureus bacteria (gram positive) were evaluated using disk diffusion and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) antibacterial tests. The inhibition growth zone formed around the antibiotic and nanocomposite 25 mg/ml under dark and light was about 32 and 14, 11 mm, respectively. Also, MIC and MBC values for final nanocomposite were 62.5 and 125 μg/ml, respectively.

Efficient removal of crystal violet dye from water using zinc ferrite-polyaniline nanocomposites

Nanomaterials are widely employed in wastewater treatment, among which nanoferrites and their composites hold significant prominence. This study adopts a green approach to synthesize zinc ferrite nanoparticles, subsequently integrating them with polyaniline (PANI) to fabricate the ZnFe2O4-PANI nanocomposite. Characterization of the prepared ZnFe2O4-PANI nanocomposite was conducted using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopic (SEM) techniques. Using Scherrer's equation, the crystallite size of the synthesized zinc ferrite nanoparticles was found to be 17.67 nm. SEM micrographs of the ZnFe2O4-PANI nanocomposite revealed that in situ polymerization of ZnFe2O4 with polyaniline transforms the amorphous surface morphology of the polymer into a homogeneous nanoparticle structure. The adsorption of crystal violet (CV) dye onto the surface of the ZnFe2O4-PANI nanocomposite depends on pH, adsorbent dosage, temperature, concentration levels and duration. The Langmuir adsorption model fitted the data well, indicating adherence to a pseudo-second-order kinetic pattern. Thermodynamic values ΔG°, ΔH° and ΔS° indicated that the adsorption process occurred spontaneously. Advantages and disadvantages of the technique have also been highlighted. Mechanism of adsorption is discussed. From the obtained results, it is evident that the ZnFe2O4-PANI nanocomposite holds promise as a sorbent for the removal of dye from wastewater.

Easy synthesis of PPy/TiO2/ZnO composites with superior photocatalytic performance, efficient supercapacitors and nitrite sensor

The synthesis of Polypyrrole (PPy)/TiO2/ZnO composites involved a chemical oxidative polymerization process, wherein the addition of TiO2/ZnO was varied from 1 to 10 wt%. The composites' photocatalytic capabilities, supercapacitor performance, and potential use as a nitrite sensor were thoroughly assessed, alongside investigations into their photoluminescence (PL) and morphological characteristics. The strong interaction between TiO2/ZnO and PPy was confirmed using FTIR, UV-Vis, and PL spectroscopy techniques. The composites demonstrated aggregated and spherical-shaped morphological features investigated by FESEM. Such morphological structures of the composites were distinct from the TiO2/ZnO (rod-like) and similar to PPy structure (spherical). However, such composites showed dominating spherical-shaped morphology ensuring a diameter in the range of 50-200 nm. The PPy/TiO2/ZnO composites exhibited significantly enhanced photocatalytic efficiency in methylene blue (MB) removal, achieving a range of 88-93% compared to PPy alone, which only achieved 77.2% MB removal. The Cyclic Voltammetry (CV) data exhibited a promising hybrid supercapacitor performance of the composites with a high capacitance value, good energy density, as well as an excellent power density. The fabricated supercapacitor was capable of lightened up a single red 5 mm LED for a few minutes, indicating the commendable energy storage capacity. A newly developed PPy/TiO2/ZnO composite is potentially used to develop as a sensor probe for the detection of nitrite chemicals using the linear sweep voltammetry (LSV) technique in three electrodes system in room conditions. It is found an excellent sensor results in terms of sensitivity as well as detection limit and satisfactory results when validated with the real samples. These results offer novel insights into the fabrication of PPy/TiO2/ZnO photocatalysts for addressing organic waste treatment, while also presenting promising prospects for potential applications in supercapacitors and sensors.

Antibacterial Carbon Dots: Mechanisms, Design, and Applications

The increase in antibiotic resistance promotes the situation of developing new antibiotics at the forefront, while the development of non-antibiotic pharmaceuticals is equally significant. In the post-antibiotic era, nanomaterials with high antibacterial efficiency and no drug resistance make them attractive candidates for antibacterial materials. Carbon dots (CDs), as a kind of carbon-based zero-dimensional nanomaterial, are attracting much attention for their multifunctional properties. The abundant surface states, tunable photoexcited states, and excellent photo-electron transfer properties make sterilization of CDs feasible and are gradually emerging in the antibacterial field. This review provides comprehensive insights into the recent development of CDs in the antibacterial field. The topics include mechanisms, design, and optimization processes, and their potential practical applications are also highlighted, such as treatment of bacterial infections, against bacterial biofilms, antibacterial surfaces, food preservation, and bacteria imaging and detection. Meanwhile, the challenges and outlook of CDs in the antibacterial field are discussed and proposed.

Synthesis of highly fluorescent carbon quantum dots from rubber seed shells for the adsorption and photocatalytic degradation of dyes

The potentials of biomass-based carbon quantum dot (CQD) as an adsorbent for batch adsorption of dyes and its photocatalytic degradation capacity for dyes which are congo red (CR) and methylene blue (MB) have been conducted in this study. The CQDs properties, performance, behaviour, and photoluminescence characteristics were assessed using batch adsorption experiments which were carried out under operating conditions including, temperature, pH and dosage. The morphological analysis revealed that CQDs are highly porous, uniform, closely aligned and multi-layered. The presence of hydroxyl, carboxyl and carbonyl functional groups indicated the significance of the oxygenated functional groups. Spectral analysis of photoluminescence for CQDs confirmed their photoluminescent quality by exhibiting high excitation intensity and possessing greenish-blue fluorescence under UV radiation. The removal percentage of the dyes adsorbed for both CR and MB dyes was 77% and 75%. Langmuir isotherm and pseudo-second-order models closely fitted the adsorption results. Thermodynamics analysis indicated that the adsorption process was exothermic and spontaneous, with excellent reusability and stability. The degradation efficiency of CQDs on both dyes was more than 90% under sunlight irradiation and obeyed the first-order kinetic model. These results demonstrated CQDs to be an excellent adsorbent and outstanding photocatalyst for organic dye degradation.

Photocatalytic degradation of dyes by novel electrospun nanofibers: A review

Textile industry is a significant contributor of wastewater, which contains pollutants including dye and other chemical substances. The release of thousands of tons of dye used in textile processing and finishing into natural streams and aquatic bodies present dire harm to the environment. In response to environmental concerns, a number of research have been done using low-cost technology to produce absorbents that can remove dyes from water bodies. Distinct techniques such as adsorption, enzymatic and photocatalytic degradation, etc. have been employed to remove dyes. In the last few decades, photocatalysis, a simple and green strategy, has emerged as the most valuable and recent principle that deals with wastewater treatment, using uniquely fabricated nanomaterials. Among them, rapid and versatile electrospinning methods have been used for the construction of a large surface area, hierarchical and reusable nanofibers for environmental remediation. As a flexible and fast fabrication method, reviewing the use of electrospun photocatalytic nanofibers, influential parameters in electrospinning and their effectiveness in the generation of oxidizing agents are a promising platform for the fabrication of novel nanomaterials in photocatalytic degradation of dyes. This review discusses techniques for dye removal, electrospun nanofibers, their fabrication and application in photocatalysis; mechanism of photocatalytic degradation, and challenges and suggested remedies for electrospun nanofibers in photocatalysis.

Chitosan functionalized bismuth oxychloride/zinc oxide nanocomposite for enhanced photocatalytic degradation of Congo red

The industrial discharge of dye pollutant contaminated wastewater is the major cause of water and soil pollution. Photocatalysis is a promising and green remediation technology, which has received widespread attention in the remediation of hazardous dyes from aqueous environment and convert them into harmless compounds. Herein, we report the synthesis of chitosan (CS) functionalized bismuth oxychloride/zinc oxide (BiOCl/ZnO) nanocomposite by a modified hydrothermal route. The physiochemical characterization revealed that the synthesized nanocomposite have crystalline, agglomerated spherical along with rod shaped morphology and size range from 35 to 160 nm. FTIR peaks at 825, 727, 662 and 622 cm^-1 specified the presence of BiO and ZnO bonds, whereas peak at 1635 cm^-1 revealed the existence of amine groups which confirms the presence of CS in the synthesized CS-BiOCl/ZnO nanocomposite. Catalytic property of synthesized nanocomposite was evaluated by the degradation of Congo red (CR) under UV-light irradiation. CR dye degradation percentage was found to be 93 % within a short period of 40 min by utilizing UV-light. Furthermore, reusability of CS-BiOCl/ZnO photocatalyst was also investigated, and it remained significant photocatalytic activity after three consecutive cycles. Hence, the results obtained in this study revealed that CS-BiOCl/ZnO nanocomposite can be used as a potential photocatalyst to remediate organic pollutants in various industries.

Enhanced UV Protection, Heavy Metal Detection, and Antibacterial Properties of Biomass-Derived Carbon Dots Coated on Protective Fabrics

Carbon dots (CDs) were simply prepared from charcoal by hydrothermal processing at 180 °C for 15 h without any chemicals. The as-prepared CDs with an average diameter of 5 ± 6 nm exhibited a predominant absorption peak at 290 nm, corresponding to the n to π* transition of the oxygen functional groups (C═O) and the free amine functional groups (-NH₂). The resulting CDs were then incorporated into cotton and polyester by facile ultrasonication for 1 h. The obtained CD-coated fabrics were first evaluated for their UV-blocking capability and then for their antibacterial properties against two model pathogens: Gram-negative E. coli and Gram-positive S. aureus. Both cotton and polyester showed no UV protection at 280 or 380 nm; conversely, cotton or polyester decorated with CDs exhibited a UV blocking ratio of 82-98%. The CD-coated fabrics showed 100% antibacterial activities against E. coli and S. aureus, whereas the pristine fabrics showed no effect. The CDs/fabrics could adsorb Hg²⁺ and Fe³⁺, resulting in a drastic fluorescence quenching. As such, this distinct feature was exploited for the removal and detection of these two ions with the limits of detection of 55and 72 μM, respectively.

Recent Advances in the Removal of Organic Dyes from Aqueous Media with Conducting Polymers, Polyaniline and Polypyrrole, and Their Composites

Water pollution by organic dyes, and its remediation, is an important environmental issue associated with ever-increasing scientific interest. Conducting polymers have recently come to the forefront as advanced agents for removing dye. The present review reports on the progress represented by the literature published in 2020-2022 on the application of conducting polymers and their composites in the removal of dyes from aqueous media. Two composites, incorporating the most important polymers, polyaniline, and polypyrrole, have been used as efficient dye adsorbents or photocatalysts of dye decomposition. The recent application trends are outlined, and future uses also exploiting the electrical and electrochemical properties of conducting polymers are offered.

{BW12O40} Hybrids Modified by in Situ Synthesized Rigid Ligand with Supercapacitance and Photocatalytic Properties

Organic rigid ligand-modified polyoxometalate-based materials possess complex and diverse structures, promising electrochemical energy storage properties and outstanding photocatalytic capabilities. Hence, two new [BW₁₂O₄₀]^5-(abbreviated as {BW₁₂O₄₀})-based inorganic-organic hybrids [{Cu(en)₂(H₂O)}][{Cu(pdc)(en)}{Cu(en)₂}(BW₁₂O₄₀)]·2H₂O (1) and [{Cu^I₅(pz)₆(H₂O)₄}(BW₁₂O₄₀)] (2) (pdc = 2-picolinate, en = ethylenediamine, pz = pyrazine) were successfully synthesized through a hydrothermal method. Among them, pdc and pz were obtained by in situ transformation from 2,6-pyridinedicarboxylic acid (H₂ pydc) and 2,3-pyrazinedicarboxylic acid (H₂pzdc), respectively. In compound 1, the {BW₁₂O₄₀} clusters as an intermediate junction connect with {Cu(pdc)(en)}{Cu(en)₂} and {Cu(en)₂(H₂O)} to form monomers, which in turn form supramolecular chains, sheets, and space network via hydrogen bonding. The {BW₁₂O₄₀} clusters are packed into copper-pyrazine frameworks in compound 2, and a unique polyoxometalate-based metal organic frameworks (POMOFs) structure with a new topology of {12}₂{6.12³.14²}₂{6².12.14².18}{6².12³.16}{6}₆ is formed via covalent bonds. When used as electrode materials for supercapacitors, the values of specific capacitance are 651.56 F g^-1 for 1-GCE and 584.43 F g^-1 for 2-GCE at a current density of 2.16 A g^-1 and good cycling stability (90.94%, 94.81% of the initial capacity after 5000 cycles at 15.12 A g^-1, respectively). The kinetic analysis reveals that surface capacitance plays a major role. Furthermore, both compounds can effectively degrade Rhodamine B (RhB) and Methylene blue (MB), showing the outstanding photocatalytic performance.

Carbon Dots as an Emergent Class of Antimicrobial Agents

Antimicrobial resistance is a recognized global challenge. Tools for bacterial detection can combat antimicrobial resistance by facilitating evidence-based antibiotic prescribing, thus avoiding their overprescription, which contributes to the spread of resistance. Unfortunately, traditional culture-based identification methods take at least a day, while emerging alternatives are limited by high cost and a requirement for skilled operators. Moreover, photodynamic inactivation of bacteria promoted by photosensitisers could be considered as one of the most promising strategies in the fight against multidrug resistance pathogens. In this context, carbon dots (CDs) have been identified as a promising class of photosensitiser nanomaterials for the specific detection and inactivation of different bacterial species. CDs possess exceptional and tuneable chemical and photoelectric properties that make them excellent candidates for antibacterial theranostic applications, such as great chemical stability, high water solubility, low toxicity and excellent biocompatibility. In this review, we will summarize the most recent advances on the use of CDs as antimicrobial agents, including the most commonly used methodologies for CD and CD/composites syntheses and their antibacterial properties in both in vitro and in vivo models developed in the last 3 years.

Sustainable one-pot synthesis of strontium phosphate nanoparticles with effective charge carriers for the photocatalytic degradation of carcinogenic naphthylamine derivative

In this work, a sustainable one-pot precipitation method was applied for synthesizing strontium phosphate nanoparticles (SrPO NPs), which can be utilized as effective charge separation photocatalysts for the degradation of oncogenic naphthylamine derivatives (congo red).