Green perspective of N-CDs towards energy crisis and photodegradation of toxic dyes

Abstract Here we have presented a general overview of an environmental friendly, one-step, cost-effective, and efficient microwave irradiation method for the preparation of self heteroatom doped Nitrogen doped carbon dots (N-CDs) which demonstrated an average size of less than 10 nm and an interplaner distance of 0.334 nm. These N-CDs possess 2.35 eV energy gap with 65.5% fluorescence quantum yield. The surfaces of these graphitic-like structures are doped with (S, P, K, Mg, Zn) = 1% along with the extra passivating agent nitrogen (N). They have demonstrated wider absorption (between 300 and 550 nm) and emission (between 400 and 600 nm) bands and also managed enormous active surface sites and defects, that further extend its usage in energy harvesting, storage and photo catalysis owing to their unique property of electron transport and collection system. In addition, we have prepared, tested, and optimised new TiO2/N-CDs composite as photo anode and N-CDs/CB composite as photo cathode for application in dye-sensitized solar cells (DSSC). The achieved power conversion efficiency of the DSSC employed photoanode N-CDs/TiO2 and counter electrode carbon black/N-CDs, demonstrated a substantial improvement, in photo current and photo voltage owing to their multiple factor visible light absorption, effective electron separation, and longer recombination time resulted a Jsc. of 22.90 mA cm2, Voc. of 0.780 V, FF. of 74% and an overall PCE of about 13.22% approximating 2.5-fold increase in power conversion efficiency as compared to that of pure TiO2 and platinum based DSSC, where Jsc. (= 10 mA cm2), Voc. (= 0.750 V) and a total of 5.42% power efficiency. Furthermore, TiO2 was modified with Heteroatom-doped N-CDs using a novel ultrasonic immersion technique, and demonstrated greater photocatalytic activity for the degradation of methylene blue (85%) with a rate constant of 0.1068 in accordance with the pure TiO2 film and N-CDs which have showed only 20% and 30% photodegradation with lower rate constants under short UV irradiation, demonstrating the formation of reactive oxygen species and H+ ions in the sample solution resulting enhanced effective mobility of electrons and holes between TiO2/N-CDs composite nanomaterial, resulted greater photo degradation.