Currently, the technologies accompanying the usage of waste materials for the fabrication of innovative useful materials have been significantly advanced. For the same purpose, a possible sustainable approach was demonstrated for the utilization of jute caddies, known as jute industry waste. From the industrial waste, carbon dots (CDs) were sonochemically prepared, followed by their surface modification with benzalkonium chloride (BZC) to yield waste jute-derived fluorescent surface-quaternized CDs (JB-CDs), which exhibit excellent water solubility, excitation-dependent emission, and good photostability, and were utilized as a fluorescent nanoswitch to detect inorganic pollutants, such as chromium (VI) [Cr­(VI)] ions, in aqueous solutions. JB-CDs can detect Cr­(VI) concentrations as low as 0.03 μM through luminescence quenching (“turn-off”) and further recover their fluorescence (“turn-on”) selectively for sensing ascorbic acid (AA), compared with other metal ions and biomolecules tested. The present technique has the advantages of fast response time and high selectivity and sensitivity in practical applications. JB-CDs were tested against a Gram-negative bacterium, Escherichia coli, and a Gram-positive bacterium, Staphylococcus aureus, to confirm their bactericidal activity. The results indicated that JB-CDs substantially inhibited the growth of the tested bacteria. Besides this, JB-CDs played the role of a nanovehicle to exemplify the release study of a model drug ciprofloxacin. It was observed that the surface-quaternized JB-CDs showed a pH-responsive release behavior, where the release behavior was found to be better controlled at pH 7.4 than at pH 5.2 and 6.8. The synthesis of such a fluorescent nanobutton, stimuli-responsive drug release, and antibacterial nanomaterial using a sustainable material such as jute industrial waste can pave the path for a smart multifunctional material.

This work reports on the synthesis of polymers (polyaniline, polypyrrole, and co-polymerization of polyaniline and polypyrrole) from monomers using carbon dots and UV light as initiators.

The synthesis of nitrogen-doped carbon dots (N@CDs) was accomplished by a hydrothermal process using meta-phenylenediamine as a source of carbon and nitrogen. As prepared N@CDs exhibited bright blue color fluorescence emission (λ ex = 340 nm and λ em = 420 nm) with a quantum yield of 12%. Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus were eradicated by N@CDs with a minimum inhibition concentration (MIC) of 1 and 0.75 mg/mL, respectively. The N@CDs were also proven as nanovesicles for drug molecules where the drug release displayed a sustained time-dependent profile at the physiological condition. The release of ciprofloxacin as a model drug was governed by the Korsmeyer-Peppas model, indicating ∼60% of its release from the N@CD conjugated drug system at the physiological pH. Selective analysis of trinitrophenol (TNP), a popular explosive, was achieved by fluorescence quenching of N@CDs, compared favorably with other nitrophenols. An estimated detection limit of TNP was 2.45 μM with a linear response spanning from 1 to 75 μM.

Carbon dots (CDs) were obtained from medicinal turmeric leaves (Curcuma longa) by a facile one-step hydrothermal method and evaluated for their bactericidal activities against two gram-negative; Escherichia coli, Klebsiella pneumoniae, and two gram-positive counterparts; Staphylococcus aureus, S. epidermidis. The CDs exhibited spherical shapes with a mean size of 2.6 nm. The fluorescence spectra of CDs revealed intense fluorescence at λex/em = 362/429 nm with a bright blue color in an aqueous solution. The CDs showed strong photostability under various environmental conditions (pH, salt, and UV-radiation). The complete bactericidal potency of CDs was 0.25 mg/mL for E.coli and S. aureus after 8 h of exposure, while for K. pneumoniae, and S. epidermidis, the CDs at 0.5 mg/mL good antibacterial effect within 8 h and complete eradication after 24 h of exposure is observed. The release of reactive oxygen species played a crucial role in the death of the bacterial cell. The present study provides a strategy for the preparation of CDs from a medicinal plant and their potential antibacterial activities against four common contagious pathogens.

The carbon dot initiated polypyrrole (PPY) and CuO composite were synthesized into PPY@CuO using a simple one-step sonochemical approach. The synthesized PPY and the PPY@CuO were characterized using Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, 13C-solid-state nuclear magnetic resonance (NMR) spectroscopy, UV–visible spectroscopy, and scanning electron microscopy. A strong interaction was demonstrated between the PPY chains and CuO. This interaction led to changes in the backbone chain of the PPY@CuO composite when compared to the carbon dot initiated PPY. The antibacterial activity against Escherichia coli and Staphylococcus aureus of the carbon dot initiated synthesis of PPY and the sonochemically prepared PPY@CuO composite materials was revealed. The results indicate the biocidal efficacy of PPY@CuO on both Gram-positive and Gram-negative bacteria. The PPY@CuO composite exhibited an enhanced antibacterial performance in comparison with the carbon dot initiated PPY and CuO. This is a first report on the sonochemical synthesis of a polymer composite composed of PPY and CuO, demonstrating the efficacy of its antibacterial action at a concentration of 1 mg/mL of the composite involving 0.234 mg/mL of CuO.

A simple one-step process for the polymerization of dopamine has been developed using nitrogen-doped carbon dots (N@C–dots) as the sole initiator. The synthesized amorphous polydopamine (PDA)-doped N@C–dots (PDA–N@C–dots composite) exhibited a negative charge of –39 mV with particle sizes ranging from 200 to 1700 nm. The stable colloidal solution was active against methicillin-resistant Staphylococcus aureus (MRSA), a Gram-negative bacterium. The strong adhesion of the polymer to the bacterial membrane resulted in a limited diffusion of nutrients and wastes in and out of the cell cytosol, which is a generic mechanism to trigger cell death. Another possible route is the autoxidation of the catechol moiety of PDA to form quinone and release reactive oxygen species (ROS) such as superoxide radicle and hydrogen peroxide, two well-known ROS with antimicrobial properties against both Gram-negative and Gram-positive bacteria.

This work unraveled kinetics, isotherm, and thermodynamic properties of methylene blue (MB) adsorbed on polyaniline (PANI) and polypyrrole (PPY). The two polymers, PANI and PPY, synthesized by a facile C-dot (CD)-initiated polymerization method have been proven as the effective adsorbent materials to remove MB from wastewater. This dye model is also generally employed as a redox indicator in analytical chemistry and exhibits blue in an oxidizing environment, but it is colorless when exposed to a reducing agent. The effects of temperature, adsorbent amount contact time, and dye concentration were consistently examined. The adsorption capacity of the polymers at 28 °C could reach 19.2 mg/g. The adsorption equilibrium of the dye was attained after 90 and 120 min of contact time with PANI and PPY, respectively. The equilibrium details were well described by Freundlich and Langmuir isotherms. Results showed that PANI and PPY prepared using CD-initiated polymerization are better adsorbents compared to the commercial PANI powder for the removal of MB from water.

A polydopamine (PDA) composite was synthesized by depositing Zn-doped CuO (Zn@CuO) particles on polydopamine by one-step ultrasonication. XPS, XRD, and FTIR confirmed the formation of spherical Zn@CuO on PDA with resulting diameters ranging from 1 to 5 μm. The PDA-Zn@CuO at 0.125−0.5 mg/mL exhibited a superior activity over Zn@CuO against sensitive and antibiotic-resistant bacteria. The Zn@CuO nanosized hybrid particles could penetrate the cell but interacted less effectively with bacterial biomolecules to provoke rapid cell lysis. PDA above 0.5 mg/mL also had a modest effect against Escherichia coli and Staphylococcus aureus. However, much higher PDA concentrations were required to restrict the flow of essential nutrients and wastes in and out of the cytoplasmic matrix and resulted in eventual cell death. The binding of PDA-Zn@CuO to bacteria played an important role in causing bacterial death, whereas reactive oxygen species (ROS) also effectively contributed to cell killing.