عنوان مقاله [English]
Environmental pollutants in industrial effluents such as organic dyes and other chemical compounds have many destructive effects on human health, other living organisms, and the ecosystem nature. Toxic dyes are considered a major source of global environmental pollution problems. So, research on the removal and reduction of these pollutants is of great interest. In this study, first, nanocrystalline cellulose (NCC) was synthesized from microcrystalline cellulose using high‐intensity ultrasonication as a mechanical method without any chemical treatment and the use of acidic corrosive substances. Then Cu/nano cellulose (Cu/NCC) nanocomposite was synthesized using nanocrystalline cellulose as support and ascorbic acid and hydrazine as reducers. The structure of as-prepared nanocomposite was characterized by various analyses such as ultraviolet spectroscopy (UV), infrared spectroscopy (IR), scanning electron microscope (SEM), energy-dispersive x-ray spectroscopy (EDX), and x-ray powder diffraction (XRD). The catalytic activity of the nanocomposite was investigated in the removal reaction of methyl orange (MO) and 4-nitrophenol (4-NP) organic pollutants. The results demonstrated the catalytic removal of methyl orange and 4-nitrophenol in a short period (210-330 s) with a rate constant (0.0041 – 0.0063 s-1), respectively. The use of nanocrystalline cellulose as a substrate and ascorbic acid as a reducing agent in the synthesis process, which are environmentally friendly, and the appropriate catalyst efficiency, and reduction of dye removal time are the advantages of this work.
In today's life, due to changes in lifestyle and the industrialization of societies, the risk of increased environmental pollution, especially organic pollutants resulting from industrial effluents, threatens the health of humans and other living things. Accordingly, the effort to remove pollutants from industrial wastewaters has become one of the most important issues for many scientists around the world. Organic dyes are known as one of the most harmful and widely used pollutants in industrial effluents, and research has shown that 700,000 tons of dyes are produced every year, most of which are azo dyes - dyes with at least one azo group (R1 – N = N – R2) - is assigned (Ravikumar et al. 2018). Methyl orange as an azo anionic dye is widely used in the paper-making, printing, cosmetics, and dyeing industries. This dye is highly toxic and due to its biodegradable nature is one of the biggest ecological hazards and has very destructive effects on human health and other organisms (Heidari & Aliramezani 2021; Ravikumar et al. 2018).
4-nitrophenol is widely used as one of the most resistant pollutants in various industries such as pharmaceuticals, paper production, petrochemicals, fungicides, pesticides, insecticides, preservatives, explosives, and dyes (Heidari & Karbalaee, 2019). Due to high toxicity, very high stability in the environment, as well as very good solubility in water, compared to other phenol derivatives, it has many detrimental effects on the environment and the health of organisms and causes severe irritation of the eyes, skin, and respiratory system. However, 4-aminophenol, which is obtained from the reduction of this pollutant, is of great commercial importance as an intermediate for agricultural chemicals, pharmaceuticals, pigments, and other industrial products (Liu et al. 2016).
On the other hand, using noble metal catalysts such as Au, Pt, Ag, Ni, due to their high catalytic activity and optimum selectivity, is very common. But the utilization of Cu due to the reasonable price, high efficiency, compatibility with the environment and body of living organisms, and very high stability has been suggested. (Jiang et al. 2018; Kgatle et al. 2020)
In this research, an attempt has been made to prepare nanocrystalline powder from micro cellulose powder and use it as a substrate by using a simple and green method without using toxic and common corrosive chemicals such as sulfuric acid. Copper metal composite on the basis of nanocrystalline cellulose (Cu/NCC) was synthesized using ascorbic acid as a green reducing agent. It can be used as an effective catalyst in the catalytic reduction of organic pollutants of orange methyl and 4-nitrophenol in an aqueous solution.
• Synthesis of nanocrystalline cellulose
First, 3 g of microcrystalline cellulose powder was weighed and 100 ml of deionized water was added to it. The mixture was stirred magnetically for 24 hours at room temperature. After placing it in an ice bath in an ultrasonicator for 15 minutes, then place the suspended mixture in a centrifuge for 4000 rpm, and dry at 60 °C (Heidari & Karbalaee, 2019).
• Synthesis of cellulose/copper nanocrystalline composite (Cu / NCC)
0.2 g of the nanocrystalline cellulose with 20 ml of deionized water was mixed for 20 minutes, then 40 ml of 0.1% copper sulfate and 1 ml of 0.02 M ascorbic acid was gradually added and refluxed in an oil bath at 110 °C. After 20 minutes, 2 ml of NaOH 2 M was added and reflux for another 20 minutes. After the second 20 minutes, 1 ml of 35% hydrazine was added to the solution drop by drop, and a sharp change in color from light green to brick was observed, The mixture was refluxed for 30 minutes. The precipitate was removed and placed in a vacuum oven at 60 ° C for 24 hours to dry completely. To obtain the nanocrystalline / copper (CuNP / NCC) product (Goswami & Das, 2018).
• Catalytic reaction of cellulose/copper nanocomposite in the removal of organic pigments:
0.25 ml of organic dye (methyl orange, 4-nitrophenol), 20 mM and 0.25 mL of 5 mM sodium borohydride, and 19 mL of deionized water were mixed, then 44 mg of catalyst was added. The UV-Vis absorption spectra were recorded at a constant time interval (30 s).
In summary, in this study, nanocrystalline cellulose was prepared without any chemicals and only by a mechanical method using ultrasonication and used as a green and biodegradable support for the copper nanoparticles synthesis. As-prepared nanocomposites showed the high catalytic activity for reduction of organic pollutants including Methyl orange (MO) and 4-nitrophenol (4-NP) in a very short time in the presence of additional sodium borohydride with quasi-first-order kinetics. The use of this nanocomposite as a new, environmentally friendly, green, and cost-effective catalyst expands the use of nanomaterials to protect the environment.