Research proposal for Synthesis and characterization of Cellulose-based semiconductor aerogel Photocatalyst for water splitting and wastewater degradation.
Purpose and Motivation
The increasing environmental pollution and rapid energy shortages due to heavy development of industrialization and Water contamination have become the two serious issues worldwide. Today a major problem about water pollution is the residual dyes from different sources like pharmaceutical industries, textile industries, paper, and pulp industries, dye, and its intermediate industries, tannery and bleaching craft industries etc. These industries introduced a wide range of toxic organic pollutants into our natural water resources. Textile wastewater and other industrial products contain organic pollutants such as formaldehyde, azo dyes, dioxins, pesticides, and heavy metals, that can cause severe risk to humans and the environment [1, 2]. These mentioned organic chemicals are designed to be resistant to microbial, thermal, and chemical degradation. Most of these organic dyes used are carcinogenic and can cause severe health problems in humans and sea species.
The wastewater from textile and other industries is drained into the sea water the aquatic animals either die or contain these toxic organic pollutants in their flesh. When humans eat these affected animals, it causes cancer of lungs and other related diseases. With the growing demand for environmental remediation, pollution free-technologies and alternative energy supplies have attracted extensive research interest. In the past era, different strategies have been used to develop efficient and green technology for the degradation of highly toxic pollutants to non-toxic species. In line with the improvement of the living standards, it is very much needed to work on the degradation of these organic pollutants. These organic dyes can be treated by the Advanced Oxidation Process (AOPS).
One of them is by the use of semiconductor-based photocatalyst to decolorize and to fully degrade the azo dyes . First and most investigated semi-conductor TiO2 works only in the UV region of light. In spite of extensive efforts to dope TiO2 with metallic and non-metallic elements, its photo-responsive activity in the visible light has remained low [4-6]. In previous literature, many reports have been published on Cu2O, ZnO, Fe2O3, CuS, g-C3N4 nanocomposites, that work in visible light irradiation but impose some negative factors such as catalyst recovery is not easy. Among the novel AOPs, the heterogeneous photocatalytic oxidation process using Sulfide semiconductors is of special interest, specifically when visible light irradiation is concerned. These semiconductor photocatalysts are in powder form, which means another process of catalyst recovery is required after water treatment. Therefore, a considerable amount of research work is underway to improve the photodegradation process by making a variety of composite semiconductor materials on different catalyst carrier/support materials. This way it will be easy to recover the catalyst from treated water and the catalyst support material will add up some extra properties to the accommodated composite photocatalyst.
My study will focus on the idea to prepare a photocatalyst cellulose based semiconductor aerogel to degrade organic dyes and hydrogen production. Cellulose-based aerogel is a new concept to work on. If we use it in a cellulose-based aerogel then it can be easily recovered from treated water without imposing an extra financial burden for catalyst recovery.
- Synthesis of semiconductor photocatalyst in cellulose-based aerogel (CBA),
- To degrade hazardous organic dyes from wastewater to find a way to avoid the powder form of the catalyst that is a bit difficult to operate on an industrial level.
- To replace the powdered photocatalyst because it can cause damage and corrosion to the pumps.
Cellulose Aerogel against Dyes and its compatibility with Photocatalyst
Cellulose having chemical formula (C6H10O5) n can be sourced from many types of origin such as plants (cotton, rice husk, banana rachis, and sugarcane bagasse) [7-10]. It is cost saving renewable source, hydrophilic, eco-friendly and has high compatibility with nanoparticle photocatalyst materials . It has abundance in hydroxyl groups and provides high surface area for photocatalytic activity. Cellulose aerogel also creates a highly compatible environment to hold photocatalyst nanoparticles in its 3D structure . It is water-insoluble and tough natural fibrous polymer because of its complex inter and intramolecular hydrogen bonds. The intermolecular and intramolecular hydrogen bonding allows very packed molecular arrangement which is responsible for the formation of three-dimensional web and crystal-like structures. The elementary single cellulose fibril is accumulated onto each other which creates the aggregation of microfibrils cellulose chain fibers due to strong affinity of hydrogen bonds. The chain fibers of cellulose are resulted by the aggregation of cellulose molecules to microfibrils that may create either crystalline (higher ordered) or amorphous (less ordered) forms. Cellulose can be classified in terms of its structure as nanofiber (CNFs), nanocrystalline cellulose/cellulose nanocrystals (NCCs)/(CNCs), cellulose acetate, bacterial cellulose, regenerated cellulose (RCs) and cellulose hydrogel/aerogels. All of the above have shown brilliant compatibilities with photocatalyst materials . Therefore, the selection of the kind of cellulose has direct impacts on the catalysts it holds, in its structure, forming a new cellulose/semiconductor hybrid.
In previous reports, cellulose hydrogels showed a quite high adsorption capacity against methylene blue and acid blue due to its 3D porous structure. Cellulose is also recognized as an excellent bio-adsorbent candidate for the removal of organic dyestuff [13, 14]. Cellulose has an excellent hydrophilic property, because of its abundance in electron-rich hydroxyl groups on its structure that actually interacts with a photocatalyst by electrostatic interaction [12, 15, 16]. The advantage of superfine cellulose structure is that it actually provides mechanical support and also help to disperse inorganic nanoparticles by providing the templated surface area for proper nucleate precipitation. Cellulose nanofiber (CNF) provides an attractive suspension for photocatalytic particles, because of its favorable optical and mechanical properties. In the degradation process, the optical properties of cellulose-based material are extremely important for maximization of photocatalytic reaction, irradiated by a light source within the matrix. Cellulose possesses optical transmittance property that can lead to the enhancement of the electron distribution and its transfer to the surface of the photocatalyst. Recently, Xiujie et. el successfully penetrated xylan-CuS NPs in (CNF) cellulose structure to make composite paper for NIR induced ablation of pathogen microorganisms . Morawski and co-workers successfully made cellulose-TiO2 nanocomposite that works in UV-Vis light irradiation . The band gap of the resultant nanocomposite was 3.09 eV, causing better photocatalytic degradation efficiency. For instance, CaCO3 decorated cellulose was also prepared by in situ precipitation of CaCO3 into the cellulose Aerogel for removal of Congo Red dye . In another study, a nanocomposite hydrogel was formed by in situ reductions and oxidation of Ag3PO4 in the cellulose matric which helped to degrade rhodamine B in visible light irradiation . The cellulose aerogel structure has cavities to accommodate the particles of Ag3PO4. Similarly, another study was carried out in which Cu2O nanoparticle functionalized cellulose-based aerogel (Cu2O/CBA) (Cellulose Based Aerogel) with three dimensional (3D) microporous structure having abundant active sites was successfully formed to work in visible light irradiation .
In this study, the feasibility of Copper based composite material in cellulose aerogel was confirmed as shown it figure 5, we can see that the deposition of Cu2O particles on inner walls of cellulose structure. By increasing the concentration of CuSO4, the amount of Cu2O deposition was also increased. The adsorption and photocatalytic activity of Cu2O-b-CBA successfully degraded methylene blue.
All the above studies encourage the possibility to make cellulose based CuS aerogel which can possibly work well to degrade MB. To use cellulose for CuS with H2O2, it is a challenging task. Because the decomposition of cellulose may occur in hydrogen peroxide environment. But based on a report published elsewhere, it was confirmed that the Fenton like reactions were successfully carried out with NanoFibril (CNF) Cellulose aerogel-based catalyst in presence of H2O2 .
- Synthesis of Cellulose Aerogel
Approach 1: Cellulose nanofibril (CNF) can be synthesized from wood Kenaf core powder as per a previously reported study . Kenaf core powder can be rinsed with water (Distilled) to remove all impurities and then it can be dignified several times by bleaching it with acid-chlorite to obtain cellulose. Defibrillation of it can be carried out using a high-speed blender, by addition of 0.1mM NaCl as a counter ion with 0.7 wt% of cellulose. The produced CNF can be freeze-dried if required for making its aerogel.
Approach 2: The process involves dissolution and gelation steps. An option to make (RC) aerogel chemically is reported in past . Whereas, another approach is to produce a Nanoporous aerogel using Nano fibrillated cellulose (CNF) by using a freeze-drying method . Cellulose powder of size 20 µm (2g) can be dissolved in 7wt% of NaOH /urea 12wt% (66g) to get cellulose solution . Addition of ammonium persulfate (0.2g) to produce free radicals was carried out for 15 minutes at room temperature. Then acrylic acid (10g), Acrylic amide (2g) and N, N-methylene bisacrylamide (0.6g) were added into the solution and then it was kept in the freezer for 24 hours at negative 20 degree Celsius temperature to conduct polymerization. Then the obtained samples were washed with ethanol and freeze-dried to get cellulose aerogel.
Formation of Semiconductor photocatalyst
The semiconductor photocatalyst can be prepared according to the requirement and then it is added in the prepared Aerogel in suitable conditions and Solvents
- Similar Work and Conclusive Statement
Recently, a successful study on nitrogen-doped TiO2 on S-PS (Syndiotactic Poly Styrene) polymer based aerogel is reported , degrading non-biodegradable organic dyes in visible light irradiation. This study demonstrates the possibility of holding the photocatalyst nanocomposite material in aerogel cavities of a synthetic polymer. The study also reveals the fact that the efficiency of aerogel-based photocatalyst was increased because of the high surface area and better optical properties. Another approach to immobilize TiO2 in the cellulose matrix (obtained from cotton linter pulp) was used for the photocatalytic degradation of phenol under UV light irradiation . This study opened up the new possibilities for using the Cellulose-based material as a nanocatalyst carrier. Similarly, cellulose was used in another successful attempt when CaCO3 was decorated on cellulose aerogel that aided the removal of Congo red . By this report, it can now be clearly stated that cellulose aerogel finds its useful application in the photocatalytic field. Furthermore, another report on the formation of Cu2O nanoparticle functionalized cellulose based aerogel was found . Formation of Octahedral Cu2O NPs was observed that anchored onto the surface and inner walls of the cellulose matrix. The photodegradation performance of Cu2O/CBA (Cellulose Based Aerogel) was remarkably efficient against Methylene blue (MB).
No further work has been reported yet in this field featuring cellulose as an aerogel carrier for a photocatalyst. Material science and environmental science applications are the top two areas where cellulose-based material find their applications but the total number of publications are 4% and 3% respectively. If we try to narrow down the search term by writing “Photocatalyst and Cellulose”, then the number of results are very inadequate. The formation of renewable, cheaper and environmental friendly photocatalyst/cellulose hybrid on a larger scale is the current consideration among the scientific community [18-20, 25].
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