Carbon quantum dots (CQDs), the newest member of carbonaceous nanomaterials, have drawn many considerations since the past two decades. A vast number of researchers made their efforts to demystify optical behavior of these materials despite being demanding. Nevertheless, their emission origin is still a controversial issue and this area suffers from a lack of hypothesis to explain the radiative transitions of these materials. White emissive CQDs are more prized among the other ones since it has provided an affordable warm white light source for many applications. In this paper, white emissive CQDs samples were prepared through a one-step hydrothermal synthesis approach. By using the advantage of possessing cellulosic networks in the Aloe Vera gel an in-situ matrix was created to encase CQDs particles. During the formation of CQDs particles, they were entrapped and created RGB nanoemitters in the cellulosic units. The leakage of the emitted photons during the radiative transitions followed by inner-filter effect (IFE) and self-/re-absorption acted as white light emissive sources. To scrutinize the validity and possibility of the hypothesis given in this paper, a series of spectroscopic analyses, including transmission electron microscopy (TEM), surface-enhanced Raman scattering (SERS), Fourier Transform Infrared (FT-IR), ultraviolet–visible (UV–Vis), and photoluminescence (PL) were conducted.

To solve the problem of water pollution, researchers have proposed a photocatalytic degradation technology, in which the key factor is the development of efficient photocatalytic materials. Graphitic carbon nitride (g-C3N4), an n-type semiconductor, has been widely studied due to its suitable band gap (2.7 eV), low cost, easy preparation, non-toxicity, and high photostability. However, the pure-phase g-C3N4 still has defects such as low specific surface area, insufficient visible light absorption, low charge mobility, few active sites for interfacial reaction, and easy recombination of photogenerated electron–hole pairs, which leads to the lower photocatalytic activity of g-C3N4. Aiming at the problems mentioned above, this paper focus on the synthesis of g-C3N4-based composites with high photocatalytic activity via lemon juice induction method. Thiourea and lemon juice were selected as precursors, and carbon quantum dots (CQDs) as electron mediators were introduced anchoring on the surface of g-C3N4 to build g-C3N4/CQDs with compact interface. The results showed that small-sized CQDs are uniformly distributed on the surface of g-C3N4, and the g-C3N4/CQDs composite has a 2D0D structure, which reduces the recombination of photogenerated electron–hole pairs. The photocatalytic degradation efficiency of 4% g-C3N4/CQDs for RhB reaches the highest data of 90.9%, and the photocatalytic degradation rate is 0.016 min− 1, which is about 2.3 times that of g-C3N4. After four cycles of photocatalytic reaction, the photocatalytic degradation efficiency of the material remained at 81.7%. Therefore, the g-C3N4/CQDs synthesized via lemon juice induction has a more stable microstructure, and the charge separation efficiency is greatly improved, which is suitable for practical photocatalytic environmental protection.

Carbon quantum dots (CQDs) as a rising class of carbon family have gained widespread attention in view of their multiple properties such as great photoluminescence (PL) properties, facile synthesis route, needing economical and cheap raw material, high physiochemical stability, and simple functionalization. This makes CQDs highly versatile and with potential for different applications. To date, CQDs-enabled photocatalysts are regarded as one of the most efficient technologies to degrade pollutants in water; however, poor activity under visible light and the recombination of photogenerated electron and hole pairs hinder getting an ideal performance that may be applied on a large scale. Conventional techniques have been modified via a new advanced method. In this review, we highlighted the strategies to improve the activity of conventional semiconductor photocatalysis via coupling with CQDs, and strategies to improve the photocatalytic activity such as functionalization, doping, and Z-scheme heterojunctions were discussed in detail. This review also covered the CQDs heterojunction application in pollutant degradation and discussed several examples with high-performance photocatalytic activity.