This work involves the development of a novel waste-derived carbon dots (CDs) conjugated with silver (Ag) nanohybrid system-based Fluorescence Resonance Energy Transfer (FRET) sensor for the detection of melamine. CDs and Ag nanoparticles served as energy donors and energy acceptors, respectively. CDs were synthesized from orange peel waste through a combined hydrothermal and ultra-sonication route. The synthesized CDs had hydroxyl, amino, and carboxyl groups on their surface, explaining that waste-derived CDs can act as reducing and stabilizing agents and showed strong absorption and fluorescence emission at 305 and 460 nm, respectively. The bandgap, linear refractive index, conduction band, and valance band potential of CDs were observed to be 2.86, 1.849, 1.14, and 4.002 eV, respectively. No significant difference was observed in the fluorescence properties at different pH (acid and alkaline) and ionic concentrations. Given their fluorescent nature, the synthesized CDs were used for the detection of melamine. The fluorescence of CDs was found to be quenched by Ag+ due to the FRET energy transfer between CDs to Ag. Notably, the zeta potential of Ag@CDs was changed from − 28.7 mV to − 30.6 mV after the incorporation of Ag+. Ag@CDs showed excellent selectivity and sensitivity toward the sensing of melamine in the aqueous solutions with the limit of detection ~ 0.85 μM. Increasing the melamine level also raises the FL intensity of Ag@CDs. The substrate was effectively used in the detection of melamine in milk as a real application and the recovery percentage was found to be 98.03%. Moreover, other adulterants such as urea and formaldehyde can be detected selectively by Ag@CDs. Overall, the synthesized Ag@CDs can be used as an efficient material for sensing applications involving such food adulterants.

Activated non-graphitizable hard carbon using orange peel with mesoporous structure has been prepared by pyrolyzation at 700, 800, 900 °C using chemical activation method. The activated orange peel-derived hard carbon has been characterized for its mesoporous and disordered structure. TG-DSC gives the information for the changes about sample composition and thermal stability of the materials. Increasing the carbonization temperature for orange peel precursor using NaOH as activating agent, elevates the pore diameter, which thereby facilitating the insertion of Na+. Raman and X-ray diffraction confirms the presence of disordered carbon. The surface morphology of the material was analyzed by scanning eletron microsope and nitrogen ( N2) adsorption and desorption analysis give the morphology, mesopore size (3.374, 3.39 and 4 nm) and surace area (60.164, 58.99 and 54.327 m2/g) of the orange peel-derived hard carbon. Hence, this work strongly evidences that the biomass-derived hard carbon with good porosity and paves way of superior electrochemical performance for emerging sodium ion batteries.

The carboxylated multi-walled carbon nanotubes (MWCNTs–COOH) were used as adsorbent for the separation of flavonoids (naringin and rutin) from bitter orange peel. The influence of the parameters such as, pH values, contact time, and desorption conditions was investigated. The samples were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, derivative thermogravimetric, scanning electron microscopy, UV–Vis spectroscopy, and high-performance liquid chromatography. After separation and desorption process, the eluent was injected for chromatography analysis. Under the optimal conditions, experimental results showed that the extraction efficiency of rutin was higher than naringin and other compounds. Moreover, the desorption percentage of flavonoids was calculated 83.6% after four cycles. This research confirmed that this method for separation of flavonoids is simple and less cost. In addition, the separated flavonoids can be used as antioxidant for the future applications.

Orange peel (OP) exhibits a sorption capacity towards anionic dyes such as reactive blue 19 (RB19). Cetyltrimethylammonium bromide (CTAB) as a cationic surfactant was used to modify the surface nature of OP to enhance its adsorption capacity for anionic dyes from an aqueous solution. Four adsorbents were investigated: the OP, sodium hydroxide-treated OP (SOP), CTAB-modified OP and CTAB-modified SOP. The physical and chemical properties of these sorbents were determined using nitrogen adsorption at 77 K and by scanning electron microscope and Fourier transform infrared spectroscopy techniques. The adsorption of the RB19 dye was assessed with these sorbents at different solution pH levels and temperatures. The effect of the contact time was considered to determine the order and rate constants of the adsorption process. The adsorption data were analyzed considering the Freundlich, Langmuir, Elovich and Tempkin models. The adsorption of RB19 by the assessed sorbents is of the chemisorption type following pseudo-first-order kinetics. CTAB modification brought about a significant increase in RB19 adsorption, which was ascribed to the grafting of the sorbent with a cationic surfactant.

UV-C와 -B type의 lamp를 이용한 혼합 자외선(UV)조사의 조사시간, 조사온도 및 광 촉매제인 H2O2의분사농도변화를 이용하여 감귤껍질에 부착되어있는 농약을 제거하기 위한 공정의 최적화를 이루고자 하였다. Chloropyrifos에 대한 독립변수들의 영향력은 조사온도가 가장 컸으며 그 다음 조사시간, H2O2 분사농도 순 이었다. Methidathion은 조사시간이 가장 컸으며 조사온도, H2O2 분사농도 순으로 나타났다. EPN은 조사온도와 조사시간이 비슷하게 나타났고 H2O2 분사농도가 가장 작았다. UV감귤껍질의 농약 잔존량이 가장 작게 나타난 처리조건으로 chloropyrifos와 EPN에 대한 최적조건으로는 조사시간 60분, 조사온도 45oC, H2O2 분사농도 1000 ppm으로 나타났다. 반면에 methidathion의 경우에는 최적조건으로는 조사시간 60분, 조사온도 40oC, H2O2 분사농도 1000 ppm으로 나타났다. 최적공정조건에서 chloropyrifos, methidathion 및 EPN의 잔존 량은 조사 전의 각각 46, 49 및 28% 수준이었다.