The isolation of nanocellulose has been extensively investigated due to the growing demand for sustainable green materials. Cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs), which have the same chemical composition but have different morphology, particle size, crystallinity, and other properties depending on the precursor and the synthesis method used. In comparison, CNC particles have a short rod-like shape and have smaller particle dimensions when compared to CNF particles in the form of fibers. CNC synthesis was carried out chemically (hydrolysis method), and CNF synthesis was carried out mechanically (homogenization, ball milling, and grinding), and both can be modified because they have a large surface area and are rich in hydroxyl groups. Modifications were made to increase the adsorption ability of heavy metal ions. The Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric (TG), and dynamic light scattering (DLS) can reveal the characteristics and morphology of CNCs and CNFs. The success and effectiveness of the heavy metal adsorption process are influenced by a few factors. These factors include adsorbent chemical structure changes, adsorbent surface area, the availability of active sites on the adsorbent’s surface, adsorption constants, heavy metal ionic size differences, pH, temperature, adsorbent dosage, and contact time during the adsorption process. In this review, we will discuss the characteristics of CNCs and CNFs synthesized from various precursors and methods, the modification methods, and the application of CNCs and CNFs as heavy metal ion adsorbents, which includes suitable isotherm and kinetics models and the effect of pH on the selectivity of various types of heavy metal ions.

Hydroquinone (1,4-dihydroxybenzene) is an aromatic organic phenolic compound used in drug and should not be used as cosmetic products. Although the use of hydroquinone has been banned in cosmetics, it is still found at low concentration for skin whitening. The effect for excess use of hydroquinone can cause irritation and changes in skin color become blackish permanently. The determination of hydroquinone can be performed by a flow injection system with spectrophotometric detection based on the redox reaction between hydroquinone and iodine. Under this method, hydroquinone can be determined based on the decreasing intensity of the blue color of the starch-iodine complex when hydroquinone was added to the solution. Hydroquinone will react with the excess iodine, thus iodine is reduced to iodide. The rest of iodine which does not react with hydroquinone, will form a blue complex with starch in an acidic condition (pH = 1). The blue color of the starch-iodine complex was analyzed by visible spectrophotometry at a wavelength of 628 nm. The optimum conditions for determination of hydroquinone using the flow injection system provide at 0.05 % starch and 40 mg/L iodine by the length of mixing coil of 50 cm on the flow rate of 5.8 mL/min, and a sample volume of 100 µL. Under these optimum conditions, the flow injection method showed the linearity from 0 to 15 mg/L with a correlation (R²) of 0.9941.

Silver nanoparticles (AgNPs) have become popular due to their unique properties that can be used as biosensors, composite fibers, semiconductor materials, and other medical applications. Green synthesis of AgNPs using natural reagents from plant extract offers advantages as an efficient and environmentally friendly technique by which the compounds from the extract perform as bio-reductor for silver ions and the capping agent for stabilizing the AgNPs. Therefore, the purpose of the study was to conduct the synthesis of AgNPs by utilizing an extract of Capsicum chinensie Jacq as the bioreductor. The effect of extract concentrations, duration of exposure to sunlight, and temperatures on AgNPs formation was studied to obtain the optimum synthesis condition. The biosynthesized AgNPs characteristics were analyzed using UV-Vis Spectrophotometry, FTIR, SEM, X-Ray Diffraction, and PSA. The results showed that the higher extract concentration produced smaller AgNPs. The synthesis under sunlight exposure showed more product of AgNPs compared to heating on a hot plate. The optimum conditions of biosynthesis of AgNPs were attained at the volume ratio of extract (20%) and AgNO3 (1mM) of 1:1 and duration of sunlight exposure of 90 min, resulting in AgNPs characterized with maximum wavelength 422 nm and average particle sizes of 67.94 nm.

The μPADs with natural reagent of Rosa damascena flower extract can be used as non invasive diagnostic of iron deficiency anemia.