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The current research mainly focuses on transforming low-quality waste into value-added nanomaterials and investigating various ways of utilising them. The hydrothermal preparation of highly fluorescent N-doped carbon dots (N–CDs) was obtained from the carboxymethylcellulose (CMC) of oil palm empty fruit bunches and linear-structured polyethyleneimines (LPEI). Transmission electron microscopy (TEM) analysis showed that the obtained N–CDs had an average size of 3.4 nm. The N–CDs were monodispersed in aqueous solution and were strongly fluorescent under the irradiation of ultra-violet light. A detailed description of the morphology and shape was established using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was shown that LPEI were successfully tuned the fluorescence (PL) properties of CDs in both the intrinsic and surface electronic structures, and enhanced the quantum yield (QY) up to 44%. The obtained N–CDs exhibited remarkable PL stability, long lifetime and pH-dependence behaviour, with the excitation/emission maxima of 350/465.5 nm. Impressively, PL enhancement and blue-shifted emission could be seen with the dilution of the original N–CDs solution. The obtained N–CDs were further applied as fluorescent probe for the identification of Cu2+ in aqueous media. The mechanism could be attributed to the particularly high thermodynamic affinity of Cu2+ for the N-chelate groups over the surface of N–CDs and the fast metal-to-ligand binding kinetics. The linear relationship between the relative quenching rate and the concentration of Cu2+ were applied between 1–30 µM, with a detection limit of 0.93 µM. The fluorescent probe was successfully applied for the detection of Cu2+ in real water. Moreover, a solid-state film of N–CDs was prepared in the presence of poly (vinyl alcohol) (PVA) polymer and found to be stable even after 72-h of continuous irradiation to UV-lamp. In contrast to the aqueous N–CDs, the composite film showed only an excitation independent property, with enhanced PL QY of around 47%. Due to the strong and stable emission nature of N–CDs in both aqueous and solid conditions, the obtained N–CDs are ideal for reducing the overall preparation costs and applying them for various biological and environmental applications in the future.

A versatile synthetic approach for development of highly fluorescent nitrogen-doped carbon dots (n-cDs) from carboxymethylcellulose in the presence of linear polyethyleneimine (Lpei) has been developed. According to single factor method, central composite design incorporated with response surface methodology matrix was applied to find and model optimal conditions for the temperature (220-260 °C), duration (1-3 h) and LPEI weight (0.5-1.5%). The statistical results show that duration was the most significant parameter for efficient carbonization conversion rate in comparison with temperature and Lpei weight. the reduced cubic model (R 2 = 0.9993) shows a good correlation between the experimental data and predicted values. the optimal variables were temperature of 260 °C, duration of 2 h and LPEI weight of 1%. Under these conditions, quantum yield of up to 44% was obtained. The numerically optimized N-CDs have an average size of 3.4 nm with graphitic nature owing to the abundant amino species incorporated into the carbon core framework. the blue-green n-cDs possess emission dependent upon the solvent polarity, wide pH stability with enhanced emission in an acidic environment. Impressively, the N-CDs show long-shelf-life for up to 1 year with no noticeable precipitation. the n-cDs were able to recognize a high concentration of fe 3+ ions with a detection limit of 0.14 μM in acidic solution owing to the special coordination for Fe 3+ to be captured by electron-donating oxygen/ amino groups around n-cDs. Moreover, the n-cDs can also be used as a new kind of fluorescent ink for imaging applications. Carbon dots (CDs) are the latest member of fluorescent carbon nano-sized family. Typically, CDs are nearly spherical-shaped nanoclusters with sizes of less than 10 nm and consist of amorphous or crystalline cores with sp 2 carbon atoms 1. Since the first established work 2 , CDs have attracted a considerable focusing in the fields of wastewater treatment, photocatalysis, bioimaging, cancer therapy and chemical sensing 3,4. This is owing to their feature of having outstanding optical properties, including excellent biocompatibility, tuneable photoluminescence, negligible toxicity, ease of production and resistance to photobleaching in comparison to QDs counterparts 5-7. It is well known that QDs, for instance, tend to be decayed in the biological environment leading to a serious toxicity concern 8 .

The grade of the environment is gradually declining especially when it comes to the severe problem of solid waste. It has become a challenging burden for many large metropolitan heterogeneous areas in most of the developing countries. The main purpose of this research is to investigate the relationship between households' attitude, descriptive norm and injunctive norm with intention to practise solid waste segregation-at-source and to ascertain the mediating effect of environmental concern and moderating effect of environmental knowledge between households' attitude, descriptive norm and injunctive norm with intention to practise solid waste segregation-at-source. The instrument is then validated from four main aspects: face validity, content validity, convergent validity and discriminant validity. After the validation process, the pre-test of this research instrument is conducted among 30 Malaysian households. All the statements have been adjusted after reliability and validity test. The final version of the instrument is set in both closed and open format which consists of eight sections: respondent's particulars (11 items), general questions on solid waste segregation-at-source (7 items), attitude (14 items), descriptive norm (12 items), injunctive norm (12 items), environmental concern (three subparts and 12 items), environmental knowledge (25 items) and intention to practise solid waste segregation-at-source (8 items). The instrument can further be used to examine other similar research areas such as sustainable consumption, recycling as well as solid waste management.

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