Carbon Quantum Dots (CQDs) have exceptionally solid and tuneable fluorescence properties which empower their application in vast fields. The hydrothermal approach is regarded as direct and efficient, through polymerization and carbonization reactions, and has been widely applied to prepare various materials due to the high reactivity of the reactants, easy control of the solution, little harm to the environment and low energy consumption under hydrothermal condition. The attracting feature of this route is that neither any strong acid nor post-synthetic surface passivation is necessary. As of now, a lot of important progress in the hydrothermal synthesis of carbon quantum dots such as materials use as precursors and influence of hydrothermal synthesis parameters. Hydrothermal synthesis is one of the most commonly used methods for preparation of nanomaterials. It is basically a solution reaction-based approach. In this review, the main focus is to review the hydrothermal route for carbon quantum dots using different source of materials and their fundamental characterizations, followed by the influence of hydrothermal synthesis conditions to carbon quantum dots.

Remazol dyes are widely used in textile industry, which are then discharged to the environment as waste products. Studies on bioremediation and decolorization of dye waste normally employ expensive spectrometers or colorimeters. This study proposes a low-cost procedure to determine the concentration of Remazol red dye with the use of a digital endoscope and image processing technique. The concentration of Remazol red dye considered in this study ranges from 0.001 to 0.700 g/L. An endoscope is used to capture digital images of dye samples. Reg-green-blue (RGB) images of the samples are converted to grayscale images, which are then converted to a mean grayscale index (MGI). The MGI is then calibrated with real concentration of dye samples. Three calibration curves were developed for three different ranges of dye concentration of 0.001- 0.010 g/L, 0.020 – 0.100 g/L, and 0.100 – 0.700 g/L, with a coefficient of determination (R2) of 0.961, 0.9793, and 0.9903, respectively.