Rapid in-situ growth of enzyme-mimicking Pd nanoparticles on TEMPO-oxidized nanocellulose for the efficient detection of ascorbic acid.

Rapid, efficient and green method of Pd nanoparticles (PdNPs) synthesis on TEMPO-oxidized cellulose nanofibril (TCNF) is demonstrated here. The nanohybrid (PdNPs/TCNF) exhibited peroxidase and oxidase-like activities evident by the oxidation of three chromogenic substrates. Enzyme kinetic studies using 3,3',5,5'-Tetramethylbenzidine (TMB) oxidation uncovered the excellent kinetic parameters (low Km and high Vmax) and good specific activities of 215 U/g and 107 U/g for peroxidase and oxidase-like activities, respectively. A colorimetric assay for ascorbic acid (AA) detection is proposed based on its ability to reduce oxidized TMB to its colorless form. However, presence of nanozyme caused re-oxidation of TMB to its blue colored form within few minutes resulting in time limitation and inaccurate detection. Thanks to the film forming nature of TCNF; this limitation was overcome by employing PdNPs/TCNF film strips that can be easily removed before AA addition. The assay allowed AA detection in the linear range of 0.25-10 µM with a detection limit of 0.039 µM. The results of AA detection in commercial beverages and vitamin C tablets are matching with the specified values. Further the nanozyme exhibited high tolerance to pH (2-10) and temperature (up to 80 °C) and good recyclability for five cycles.

Biogenic Synthesis of Carboxymethyl Cashew Gum Modified Gold Nanoparticles and its Sensitive and Selective Calorimetric Detection of Hg2+ Ions and Catalytic Reduction of Methyl Red.

In the present study, we have successfully synthesized and characterized carboxy methyl cashew gum modified gold nanoparticles (CMCG-AuNPs) via a microwave-assisted method and used as a calorimetric probe for selective detection of Hg2+ ions as well as catalytic reduction of methyl red in an aqueous medium. The effect of different parameters including concentration and irradiation time on the formation of CMCG-AuNPs was also investigated. The presence of strong surface plasmon resonance (SPR) peak in the visible region indicated the formation of AuNPs. The characterization techniques were identified the interaction between the CMCG and AuNPs with estimation of size and morphology. The face centred cubic (FCC) crystal structure was identified by using XRD and supporting with SAED pattern. TEM images of CMCG-AuNPs were exhibited as polydispersed with spherical in shape and the average particle size was 12 ± 3 nm. The synthesized CMCG-AuNPs were utilized to sensing Hg2+ ions in an aqueous medium, the presence of Hg2+ ions selectively among other metal ions, the CMCG-AuNPs were aggregated by changing the color from wine red to purple blue accompanied by change in the position of SPR peak and intensity. It was observed as a strong linear relationship based on the change in intensity, the limit of detection was determined to be 0.277 nM. The catalytic activity was also examined for the reduction of methyl red (MR) in the presence of CMCG-AuNPs was completed within 12 min and followed pseudo-first order kinetics with a rate constant of 0.261 min-1. From the obtained results, the synthesized CMCG-AuNPs were useful for detection of heavy metal ions as well as toxic pollutants degradation via a green method, and utilized sensing, environmental, and biomedical application in future.

Effective fabrication of cellulose nanofibrils supported Pd nanoparticles as a novel nanozyme with peroxidase and oxidase-like activities for efficient dye degradation.

Nanozyme-based dye degradation methods are promising for the remediation of water pollution. Though Pd nanoparticles (PdNPs) are known to act as nanozymes, their dye degradation capability has not been investigated. Low nanozyme activities, easy aggregation, difficulties in recovery and reuse are the major challenges in achieving this. For the first time, cellulose nanofibrils-supported PdNPs (PdNPs/PCNF) as a novel nanozyme with good peroxidase and oxidase-mimicking activities and easy recyclability is explored for dye degradation. An efficient and rapid method of PdNPs/PCNF preparation was demonstrated by adjusting the pH and microwave irradiation. Enzyme kinetic studies revealed good kinetic parameters and specific activities of 415 and 277 U/g for peroxidase and oxidase, respectively. PdNPs/PCNF offered 99.64% degradation of methylene blue within 12 min (0.468 min-1) with 0.4 M H2O2 at pH 5.0. Mechanistic studies revealed the involvement of hydroxyl and superoxide radicals. Owing to the network-like structure of PCNF, films and foams were prepared, their dye degradation potentials were compared, and recyclability was tested. Successful degradation of mixed dye solutions and spiked real water samples was achieved and a continuous flow method was demonstrated using a foam-packed column.

Gold nanoparticles spontaneously grown on cellulose nanofibrils as a reusable nanozyme for colorimetric detection of cholesterol in human serum.

Recently, gold nanoparticles (AuNPs) are extensively used as peroxidase mimics. However, low catalytic activity, high synthesis cost, substrate-induced aggregation in reaction medium and difficulty in recovery and reuse still remain as major challenges. Here, a novel, simple, spontaneous, and reagent-less in-situ method for the production of AuNPs using dialdehyde cellulose nanofibrils (DACNF) is proposed. AuNPs synthesis time and size were greatly influenced by aldehyde content and the optimal aldehyde content for ultra-small AuNPs (≈10 nm) was 2.1 mM/g. AuNPs@DACNFs exhibited broad-spectrum peroxidase activity and steady-state kinetics revealed their better kinetic parameters (low Km and high Vmax) over horseradish peroxidase (HRP). AuNPs@DACNFs was further converted into paper strip, which served as a biosensor for H2O2 and cholesterol detection. The proposed method exhibited wide linear response in the range of 10-90 µM and 0.05-0.45 mM, and detection limit of 0.39 µM and 1.9 µM for H2O2 and cholesterol, respectively. Great shelf life and reusability were evident by FE-SEM and ICP-OES analysis. The smartphone application "Color Grab" was used to enable the portable onsite detection. The results of cholesterol detection in human serum samples were in agreement with clinically observed values, suggesting the great potential of the probe in disease diagnosis.

Esterification of Lignin Isolated by Deep Eutectic Solvent Using Fatty Acid Chloride, and Its Composite Film with Poly(lactic acid).

In this study, the effect of lignin esterification with fatty acid chloride on the properties of lignin and lignin/poly(lactic acid) (PLA) composites was investigated. Lignocellulose (Pinus densiflora S. et Z.) was treated using a deep eutectic solvent (DES) with choline chloride (ChCl)/lactic acid (LA). From the DES-soluble fraction, DES-lignin (DL) was isolated by a regeneration process. Lignin esterification was conducted with palmitoyl chloride (PC). As the PC loading increased for DL esterification, the Mw of esterified DL (EDL) was increased, and the glass transition temperature (Tg) was decreased. In DL or EDL/PLA composite films, it was observed that EDL/PLA had cleaner and smoother morphological characteristics than DL/PLA. The addition of DL or EDL in a PLA matrix resulted in a deterioration of tensile properties as compared with neat PLA. The EDL/PLA composite film had a higher tensile strength and elastic modulus than the DL/PLA composite film. DL esterification decreased water absorption with lower water diffusion coefficients. The effect of lignin esterification on improving the compatibility of lignin and PLA was demonstrated. These results are expected to contribute to the development of high-strength lignin composites.

In-situ fabrication of novel flower like MoS2/CoTiO3 nanorod heterostructures for the recyclable degradation of ciprofloxacin and bisphenol A under sunlight.

Effectual degradation of toxic water contaminants is a crucial step in water purification and designing an efficient semiconductor based hybrid structure photocatalyst is a good approach to achieve this. Benefiting from the combination of semiconductors, a series of novel visible-light active flower-like MoS2/CoTiO3 nanorod heterostructures with excellent morphological contact interface were prepared through a facile in-situ hydrothermal process. These heterostructures were well characterized and demonstrated high photocatalytic performance for ciprofloxacin (CIP) and bisphenol A (BPA) under sunlight irradiation. Compared to pristine CoTiO3 and MoS2, the optimal catalyst (5 wt% MoS2/CoTiO3) presented 39.97 and 22.32 times higher activity for CIP degradation and 26.85 and 15.66 times higher activity for BPA degradation, respectively. This improved activity can be accounted for the effective interfacial contact which promotes the efficient charge carriers separation and reduce its recombination. The catalyst exhibited decent stability and was potentially reused for five cycles without significant loss in activity. Furthermore, based on active species scavenging experiments the plausible photodegradation mechanism is discussed in detail.

Microwave-assisted preparation of a silver nanoparticles/N-doped carbon dots nanocomposite and its application for catalytic reduction of rhodamine B, methyl red and 4-nitrophenol dyes.

In the current work, a silver nanoparticles/nitrogen-doped carbon dots (AgNPs/NCDs) nanocomposite was prepared by a microwave-assisted method that does not require additional reducing or stabilizing agents. Multiple analytical techniques were used to characterize the prepared nanocomposite. The nanocomposite exhibited a surface plasmon resonance (SPR) absorption peak at 420 nm, indicating the development of AgNPs with NCDs. Further, HRTEM results confirmed the formation of the nanocomposite with the appearance of lattice fringes of both materials. Additionally, the nanocomposite did not show any precipitation even after two months of storage. The nanocomposite exhibited high catalytic activity towards the reduction of rhodamine B (RhB, 98.83%), methyl red (MR, 97.14%) and 4-nitrophenol (4-NP, 99.95%) at ambient temperature. Besides, the kinetic analysis revealed that the reduction reaction followed pseudo-first-order kinetics and the calculated rate constants (k) for rhodamine B (RhB), methyl red (MR) and 4-nitrophenol (4-NP) were found to be 0.0296 s-1, 0.0233 s-1 and 0.029 s-1, respectively. Moreover, it is a reusable and stable catalyst for reduction reactions up to five cycles without significant loss in catalytic activity. Finally, a plausible mechanism for the reduction of pollutants is also discussed in detail. As a whole, the prepared nanocomposite might display stunning behaviour for wastewater treatment applications.

N-Doped carbon dots with pH-sensitive emission, and their application to simultaneous fluorometric determination of iron(III) and copper(II).

Simultaneous fluorometric determination of iron(III) and copper(II) without the use of any masking agent or additional treatment is achieved by using N-doped carbon dots (NCDs). The NCDs were hydrothermally prepared, have strongest excitation/emission peaks at 320/406 nm and a 47% quantum yield. Excitation-tunable emission is found to depend on solution pH values. This supports the involvement of surface states in the origin of the excitation dependent nature. The NCDs were employed as a fluorescent probe for the simultaneous determination of Fe(III) with a linear response in the 3-60 µM concentration range and a 0.31 µM detection limit (LOD). The probe also responds linearly to Cu(II) in the 0.5-15 µM concentration range and with a 56 nM LOD. With the addition of Cu(II), the absorption spectra of NCDs presented a clear decrease in the intensity at 312 nm followed by an increase at 360 nm. This is not observed in the presence of Fe(III). The fluorescence lifetime of NCDs (5.8 ns) is reduced by Fe(III) but not by Cu(II). Thus, the two metal ions can be simultaneously detected without the need for any reagents. The probe was employed to quantify Fe(III) and Cu(II) in spiked water, serum, and urine samples. Graphical abstract Schematic representation of hydrothermal synthesis of highly fluorescent N-doped carbon dots with novel pH dependent emission and their application for the simultaneous determination of Cu(II) and Fe(III) with individual ion discrimination.

Construction of in situ self-assembled FeWO4/g-C3N4 nanosheet heterostructured Z-scheme photocatalysts for enhanced photocatalytic degradation of rhodamine B and tetracycline.

Although photocatalytic degradation is an ideal strategy for cleaning environmental pollution, it remains challenging to construct a highly efficient photocatalytic system by steering the charge flow in a precise manner. In this work, a novel, highly efficient, stable, and visible light active hybrid photocatalytic system consisting of FeWO4 and g-C3N4 nanosheets (CNNs) has been successfully prepared by an in situ self-assembly solvothermal approach. Several characterization techniques were employed to study the phase structures, morphologies, optical properties, surface composition and chemical state of the as-prepared samples. SEM and TEM results demonstrated that the FeWO4 nanoparticles are uniformly dispersed on the surface of CNNs with a diameter of about 10-20 nm, which could provide maximum interfacial contact and a synergistic coupling effect between FeWO4 and CNNs. XPS and FTIR results confirmed that there was strong electrostatic interaction between FeWO4 and CNNs, suggesting the formation of heterojunctions between them. In addition, UV-DRS and PL spectroscopy revealed that the FeWO4/CNN composites exhibited increased visible light absorption and improved charge generation/separation efficiency. As a result, the photocatalytic activity of the FeWO4/CNNs was enhanced in comparison with pure FeWO4 and CNNs for rhodamine B (RhB) and tetracycline (TC) degradation under natural sunlight irradiation. The photocatalytic efficiency of the optimal FeWO4/CNN composite (10 wt% FeWO4/CNNs) for the degradation of RhB (TC) was about 13.26 (4.95) and 86.2 (31.1) times higher than that of pure FeWO4 and CNNs, respectively. Meanwhile, the 10 wt% FeWO4/CNN sample exhibits good photocatalytic stability in recycling experiments. The enhanced photocatalytic activity may be attributed to the formation of the Z-scheme system between FeWO4 and CNNs, effectively prolonging the lifetime of the photoexcited electrons generated by CNNs and the photoexcited holes generated by FeWO4, which was subsequently confirmed by the active species trapping experiments and the calculation of relative band alignments. This work opens up a new feasible avenue to synthesize visible light active Z-scheme photocatalysts for application in energy production and environmental remediation.

Facile Conversion of Toxic Cigarette Butts to N,S-Codoped Carbon Dots and Their Application in Fluorescent Film, Security Ink, Bioimaging, Sensing and Logic Gate Operation.

The present work is emphasized on converting toxic cigarette butts (CBs) into highly fluorescent N,S-codoped carbon dots by a facile hydrothermal approach and exploring their multiple applications. The as-produced carbon dots (CBCDs) exhibited bright and stable fluorescence with a quantum yield of 26% and used as a label-free probe for "on-off-on" sequential detection of Fe3+ and ascorbic acid (AA). The fluorescence of CBCDs can be significantly quenched by Fe3+ ions through static quenching and restored upon the subsequent addition of AA due to the reduction of Fe3+ to Fe2+ by AA. This nanoprobe presented great selectivity and excellent sensitivity to Fe3+ and AA with a detection limit of 0.13 and 0.2 µM, respectively. Furthermore, the nanoprobe was extended to biosystem (intracellular detection) and successfully applied for the detection of Fe3+ in real water (tap, bore, and pond) and AA in biological samples (human urine and serum). In addition, we have constructed an IMPLICATION logic gate based on these unique sensing characteristics. The "visible-invisible" and "UV-visible" property explored their use as invisible ink for security applications. Furthermore, highly photostable fluorescent polymer films were prepared by incorporating CBCDs in poly(vinyl alcohol). It is anticipated that the strong and stable fluorescence emission nature of these films might find direct or indirect applications in various optical/optoelectronic devices, ranging from fluorescent displays to light-emitting diodes.

Green synthesis of highly fluorescent nitrogen - Doped carbon dots from Lantana camara berries for effective detection of lead(II) and bioimaging.

Here, we developed a simple green approach for the synthesis of highly fluorescent nitrogen doped carbon dots (NCDs) using Lantana camara berries. Optical and physicochemical properties of as synthesized NCDs were extensively studied by using various analytical techniques. NCDs exhibited bright fluorescence with Quantum yield as high as 33.15%, which is stable to various effects like heat, pH, ionic strength and continuous irradiation. Furthermore, the NCDs presented highly selective and sensitive fluorescence response towards Pb2+ which explored their potential to serve as a label-free fluorescent probe for the effective detection of Pb2+. As developed NCDs based probe exhibited a great linear response (R2=0.998) towards Pb2+ in the concentration range of 0-200nM with a detection limit of 9.64nM. The probe further presented high precision without any interference and was successfully applied for the detection of Pb2+ in the real water and human sera (serum and urine) samples. Cytotoxicity studies on both cancerous (human breast adenocarcinoma MCF-7) and normal (Human embryonic kidney HEK-293) cell lines revealed their excellent biocompatibility. With their low cytotoxicity, strong fluorescence and excitation-dependent emission, NCDs were successfully applied as multi-colour bioimaging agents and Pb2+ detection capabilities were further evaluated in live cells.