Chitosan nano-composites applications for water remediation

Abstract Water is the most crucial element for living, and the lack of pure and clean water has increased globally. Hence, the need for water remediation from different pollutants is a must. Developing different techniques to accomplish water purification is expanding every day. Chitosan is a biodegradable and eco-friendly biopolymer which is extensively used in various applications. Here, we focus on using chitosan nano complexes with ferrites, graphene, silver, and silica nanoparticles as novel, cheap, accurate, biocompatible, reusable, and fast nano-complexes. Different synthesis protocols were used to obtain Chitosan-nano complexes. Various techniques were used to characterize and test the synthesized nanocomplexes, such as UV-Vis spectroscopy, Fourier transforms infrared spectroscopy (FT-IR), powder-X-ray diffraction (p-XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Brunauer—Emmett–Teller (BET) analysis and Inductively coupled plasma mass spectrometry (ICP-MS). The chitosan-based nanocomplexes are used for water purification and detecting different chemical pollutants such as heavy metals, organic and dyes contaminations, and eliminating different pathogenic microorganisms from the environment.


PUBLIC INTEREST STATEMENT
Researches in these fields have direct implications for public policy, as the health and well-being of individuals and communities around the world depend on our ability to develop sustainable and equitable solutions to these pressing issues.By advancing our knowledge of the impacts of pollution on our environment and health, and by studying the complex interactions between marine life and the ecosystems that support them, researches have the potential to inform decisions at all levels of government, industry, and society, and to shape a more sustainable and equitable future for all.Moustapha, Eid Moustapha is Associate Professor of Chemistry, Prince Sattam bin Abdulaziz University, Saudi Arabia, he obtained Ph.D joint supervision UMC, USA and Benha University, Egypt.

Introduction
Water is essential to every living entity and a primary ingredient sustaining life.Water is used for drinking, cleaning, industrial operation, pharmaceutical manufacturing, and agricultural work.Generally, water is a main ingredient in every biological process as well as every industrial process.The industrial revolution and the dramatic increase in the human population increases water demand (Huang et al., 2008;Westall & Brack, 2018;Wiggins, 1990).Having pure and clean water is challenging, and water scarcity is a massive problem the whole planet needs to face.There is a need for novel, cheap, fast, and efficient water remediation and purification techniques from different pollutants such as heavy metals, organic dyes, and bio-pollutants such as bacteria and fungi are essential.Most of these pollutants dramatically affect human health or the environment.Also, it is vital to reutilize the prepared complexes used for water treatment (El-Monaem EM, Omer, et al., 2022;Omer et al., 2022).
Waste treatment is a global issue that is very important to be solved.The topic of water treatment attracts many researchers, and the number of publications on this topic expands exponentially every year (Figure 1) One of the prime eco-toxicological hazards is heavy metal ions that have gained increasing attention because of their toxicity and propensity of bioaccumulation in the food chain, even at reasonably lower concentrations.The unsystematic disposal of heavy metals causes water pollution of essential resources.Because of their toxic nature, many heavy metal ions are grouped as hazardous pollutants, causing adverse effects on humans.These highly toxic heavy metal ions, such as Chromium (Cr), Cadmium (Cd), iron (Fe), mercury (Hg), arsenic (As), zinc (Zn), etc., lead to carcinogenic side effects when their concentration is higher than the permissible limits.For example, two oxidation states of Chromium commonly used in industry are trivalent chromium Cr (III) and hexavalent Cr (VI).The latter is mutagenic, teratogenic, and carcinogenic, adding to that its high mobility.The permissible limit for Cr (VI) in drinking water is 0.05 mg L −1 (Kozlowski & Walkowiak, 2002;Renu et al., 2021).
Due to the development of different industrial sectors, such as pharmaceuticals, leathers, and textiles, around 15% of heavy metals and organic dyes are released into the water.These industrial pollutants are chemically stable and not degradable in water.Using dyes in different industries is increasing every day, which eventually causes water contamination (Xia et al., 2020).Other techniques used for dyes removal from wastewater such as adsorption, which depends on adsorbents with high adsorption capacity, good mechanical resistance, and simple restoration (Anas et al., 2019;Basha et al., 2022;Chaudhary et al., 2019;Xiong et al., 2020), membrane separation (Chen et al., 2019), electrocoagulation (Sadeghi et al., 2019), Fenton oxidation (Fu et al., 2020), and catalytic reduction (Afzal et al., 2018;Gabris et al., 2022;Salahuddin et al., 2020).Finding new methods for water treatment which is simple, low-cost, and renewable with high absorption capacity is of great importance.Various techniques are used for metal ions removal, adsorption, and ion exchange.Developing carbon-and carbon-based materials to adsorb heavy metals is applicable for water remediation, but using graphene oxide suffers severe drawbacks.Graphene oxide aggregates in water and hence decreases the effective adsorption surface area (Wang et al., 2020).
Chitosan is a linear, degradable biopolymer that has been used in different applications.Chitosan is used to remove several contaminants from water and overcome graphene oxide aggregation and maintain its structural stability.Chitosan is used in various applications because of its good properties, such as its unique chemical and physical characteristics, low cytotoxicity, ease of preparation and modification, water-soluble behaviour, biocompatibility, polyelectrolyte and biodegradability (El-Monaem EM, Eltaweil, et al., 2022;Eltaweil et al., 2021;Fan et al., 2013;Z. Khan, 2020).Chitosan can be synthesized by N-deacetylation of chitin, a main constituent of shrimp, insects, and crabs' crustaceans, as shown in Figure 2 (Sarkar et al., 2019;Xu et al., 2019).
Chitin and chitosan are obtained from the shells of crustaceans, such as crabs, prawns, lobsters, and shrimps.Such shells are the primary industrial biomass source for the large-scale production of chitin and chitosan (Islam et al., 2017).
Chitosan structure contains chemically active hydroxyl and amino groups, which help their functionalization using techniques such as polymer-grafting, N-and O-hydroxylation, carboxymethylation, and amination (M.Khan et al., 2021;Soares et al., 2019).Here, we report some studies that used chitosan-based nano complexes for chemical pollutants, dye removal from water, also its applications against hazardous biological contaminations.Samuel et al. used graphene oxide/chitosan/ferrite complexes to remove Chromium Cr (VI) from an aqueous solution.Characterization of the prepared complex was done using powder-X-ray diffraction (powder-XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopeenergy dispersive X-ray (SEM-EDX) analysis, transmission electron microscopy (TEM) thermogravimetric analysis (TGA), UV-vis diffusive reflectance spectra and Brunauer-Emmett-Teller (BET) analysis.The adsorption of Chromium to the complex was confirmed by the Langmuir isotherm and pseudo-second-order kinetic model.The prepared complex shows a good adsorption capacity for Cr (VI) and recyclability up to ten repetitions (Samuel et al., 2018).The removal of Cr (VI) ions from an aqueous solution using aminated chitosan matrix with Fe 3 O 4 magnetic nanoparticles was also reported (Fu et al., 2020).The prepared nanocomplex reported magnetic properties that can be separated from the aqueous medium and showed an adsorption capacity of 119.05 mg/g.The process followed both Langmuir and Freundlich isotherm models.It also has good reuse (up to seven times).

Heavy metals pollutants
Xia and coworkers utilize Sodium-copper hexacyanoferrate to adsorb radioactive Cesium from water.Sodium-copper hexacyanoferrate shows high adsorption capacity as its cubic structure is well suited to cesium size.The efficiency of sodium-copper hexacyanoferrate in collecting Cesium has a significant drawback: the resultant powder is too small to be collected easily.Radioactive Cesium is produced from different sources, such as power reactors, and is characterized by a long lifetime, good solubility in water, and high mobility.The need for its removal from water is crucial because it has harmful effects on both humans and the environment.Also, recycled radioactive Cesium can be used to generate gamma irradiation.This study used chitosan as a nontoxic, cheap biopolymer in addition to the Fe 3 O 4 magnetic nanoparticles.The developed composite was stable, easy to collect upon magnetic field application, and with high selectivity (Xia et al., 2020).
Xiong et al. studied the remediation of antimony pollution from water, as it caused severe health problems because of its toxicity.They introduced a nano-modified system composed of chitosan, iron oxide nanoparticles, and metal-organic frameworks.Chitosan has multi-amino groups, which can chemically adsorb metal ions from the solution.Furthermore, the metal-organic frameworks have an affinity for antimony which can be separated from water by its combination with nano-Fe 3 O 4 .The authors in this study toned the solution pH and the chitosan concentration to reach the most efficient conditions for antimony removal from water.The theoretical models suggested an inner-sphere surface-binding mechanism.Furthermore, they have found that antimony removal by their modified system under alkaline conditions experiences a less interference effect from common anions presented on a solution, such as carbonate, chloride, sulfate, and nitrate ions.The produced composite showed an ability to be recovered and reused (Xiong et al., 2020).Anas et al. used the spin coating technique to form a thin layer of chitosan and hydroxylfunctionalized graphene quantum dots (HGQDs).This thin layer showed a high efficiency towards Fe +3 ions detection in concentrations as low as 0.5 ppm with high sensitivity.Monitoring the concentration of Fe +3 ions is very important as it affects human health, as its decrease causes anemia and decreased immunity, and its increase causes severe diseases such as hepatitis, chromatism, and some types of cancers.Therefore, there is a need to devolve a sensitive method to detect it.Surface morphology was studied using an atomic force microscope and it showed a uniform, smooth, homogenous thin layer and confirmed its interaction with Fe +3 (Anas et al., 2019).
Chaudhary et al. introduced an efficient fluoride removal, cheap and easily separated from an aqueous medium system based on mixed metal (Fe-Al-Mn) oxyhydroxides nanoparticles system embedded into chitosan.This system overcomes the aggregation that occurs for nanoparticles upon direct interaction of nanoparticles with fluoride in an aqueous medium.Fluoride increased concentration in drinking water causes human health problems, such as a change in the thyroid level, growth retardation, osteosclerosis, and skeletal and dental fluorosis.The need for fluoride removal from drinking water is essential.Adsorption is among the favorable techniques to decrease or remove fluoride from drinking water.Using two low-cost materials to form the composite system is a great advantage.First, the source of Mn and Al drafted from ferromanganese slag originated from steel industries and abundant laterite, which is the source of Al and Fe.Synthesis of this system was done by the co-precipitation method.They have used the Freundlich isotherm model to study fluoride's adsorption into the nanocomplex system heterogeneous surface, showing pseudo-second-order kinetics with fast fluoride adsorption (Chaudhary et al., 2019).
Chen and coworkers studied using the chitosan/Fe 3 O 4 system for magnetic nanoparticle synthesis.This system was used to eliminate coke powders in coking diesel distillate, which affects heavy or residual oil treatment.The Fe 3 O 4 /chitosan system shows a good removal of coke powder and can be reused using light petroleum (Chen et al., 2019).
Sadeghi et al. synthesized Fe 3 O 4 -TiO 2 /Chitosan nanocomposite to remove cadmium pollution from water.The nanocomposite showed good electrostatic interaction with cadmium and excellent adsorption to it.It can be reused and can be easily separated after being used (Sadeghi et al., 2019).Also, Fu et al. used polyethyleneimine-grafted Fe 3 O 4 embedded into the chitosan core to adsorb phosphate from water.Increasing the phosphate level over specific values damages the ecosystem and can cause eutrophication in aquatic organisms.For humans, it can cause chronic kidney disease and cardiovascular disease.Efficient adsorption of phosphate accrued at pH range from 3 to 4. The used composite can be collected easily from the water after being used upon magnetic field application (Fu et al., 2020).
Gabris et al. used polyaniline graphene oxide chitosan doped with cobalt oxide as a sorbent for As (V) from aqueous media.The synthesized complex was characterized using FTIR, EDS, and imaged using SEM, the adsorption capacity of As (V) was 90.91 mg/g at pH 7 and about 90%, and it was controlled by pseudo-second-order, complete removal of As(V) within 50 min (Gabris et al., 2022) Afzal et al. overcame the difficulties of separating biochar in water treatment.They used chitosan/biochar hydrogel beads to remove ciprofloxacin from aqueous solutions.The equilibrium adsorption time was 48 h, and the adsorption fit with the Langmuir model and second-order mechanism.Its value was 76 mg/g.They also tested the effect of adding some electrolytes such as NaCl, Na 2 SO 4 , and NaNO 3 on sorption capacity and only increased NaCl concentration to 30 mg/g (Afzal et al., 2018).
Eltaweil et al. took advantage of the amino group in the chitosan chemical structure.Through it, they created a Sulfacetamide-Ethylacetoacetate hydrazone Schiff-base modified chitosan and decorated this structure with a magnetic material, NiFe 2 O 4, to facilitate the collection of the adsorbent.The adsorbent capacity towards Cr(VI) was 373.61 mg/g (Eltaweil et al., 2022).
Omer et al. formulated a modified magnetic chitosan composite into beads.This is another way to create an efficient adsorbent.In these magnetic beads, the chitosan structure was modified using metal-organic frameworks (MOFs).They took advantage of the high surface area of MOFs that increased the adsorption capacity.The maximum adsorption capacity of 119.05 mg/g was obtained towards Cr (VI) ions (Omer et al., 2021).
The excellent removal efficiency of up to 86% of phosphate anions from aqueous solution was obtained in a study by Eltaweil et al.The adsorbent used in this study was Lanthanum-doped aminated graphene oxide@aminated chitosan microspheres.This study revealed a correlation between the composite's Lanthanum ratio and the phosphate anions' removal capacity (Eltaweil et al., 2023).

Dyes and organic contamination
Salahulddin et al. use Fe (III) ions to oxidize pyrrole and to initiate the polymerization of chitosan and graphene oxide as well as the in-situ synthesis of different shapes of Fe 3 O 4 .The spherical Fe 3 O 4 particles stabilize graphene, prevent its aggregation, and enhance its cytotoxicity.In addition, the presence of Fe 3 O 4 in the complex structure allows its elimination from the water after adsorption.The prepared complex shows good adsorption capacity for ponceau dye in contaminated water, as the Langmuir isotherm and pseudo-second-order kinetic model concluded.Dyes are disposed into the water because of different industry pollutants such as textiles, paint, dyeing, and dye synthesis.These dyes are light and heat stable, have high molecular weight, and have a complex structure that makes them hard to degrade naturally.Furthermore, it shows an excellent antimicrobial effect against E. coli and Fusarium fungi (Salahuddin et al., 2020).
Khan used chitosan/Au/Pd/Ag nanoparticles complex to remove acid orange 7 dye.Chitosan is used as a capping agent for metallic nanoparticles used to adsorb toxic non-biodegradable organic material dyes that can prevent light transmission onto water, heavy metals, and other water pollutants.Acid orange 7 affects the human skin, respiratory and digestive systems.In their study, he combined three metal nanoparticles to improve chemical reactivity, removal activity, and adsorption efficiency (Z.Khan, 2020).
Fan et al. used β-cyclodextrin-chitosan/graphene oxide/Fe 3 O 4 complex for methylene blue dye removal from water.Different dyes in water affect fauna and flora, and it is carcinogenic to humans.This chemically synthesized complex shows combined properties from all its components, such as the hydrophobicity of B-cyclodextrin, multi-functional groups presented in chitosan, unique surface properties of graphene, and magnetic properties of Fe 3 O 4 .The complex shows good adsorption capacity to the dye.It can be easily extracted from water after applying a magnetic field and can be regenerated without affecting the composite adsorption capacity (Fan et al., 2013).
Adsorption of methylene blue was also reported by Sarkar et al., who developed a sponge-like nanostructured for water treatment.This nanostructure comprises in situ synthesized Fe 3 O 4 nanoparticles into graphene oxide nanosheets functionalized by chitosan/polymethacrylic acid.The proposed nanostructure showed good adsorption through interconnected microchannels to methylene blue as a model for dye water pollutants, also recyclability and stability over a wide range of pHs (Sarkar et al., 2019).
Xu and coworkers introduced a nanocomplex of gold nanoparticles/chitosan/graphene oxide/Fe 3 O 2 to adsorb and detect Rhodamine from different samples such as tape water, wastewater, soft drinks, and eye shadow samples.Rhodamine is a fluorescent red pigment used in the food, textiles, cosmetics, pharmaceutical, plastic, leather industries, dyeing, and printing fields.It has some disadvantages to humans, animals, and the environment, as it irritates the skin, eyes, and respiratory system.Moreover, some tests proved its potential carcinogenicity and toxicity.The presented complex was synthesized by coating Fe 3 O 4 nanoparticles with chitosan for its stability, then reacted with graphene oxide; afterward, the gold nanoparticles were added to the nanocomplex.The optimum adsorption and detection for Rhodamine were studied using magnetic solidphase extraction and fluorescent techniques (Xu et al., 2019).Sulfamethoxazole (SMX) is an organic contaminant in the water and aquatic environment.It is a widely used antibiotic for humans and veterinarians but harms the marine environment.Soares et al. studied a magnetic biosorbent of a Fe 3 O 4 magnetic core coated with a trimethyl chitosan/ siloxane hybrid shell.This core-shell complex showed good adsorption to SMX (Sarkar et al., 2019).
Khan et al. used chitosan-coated nickel selenide as a sunlight-photoactive nanocomposite for Erythrosine and Allura red dye degradation.The photocatalyst was characterized using UV-Vis Spectroscopy, XRD, and imaged by SEM.The photocatalyst results showed a high degradation efficiency for both days, reaching up to 99% at 100 and 120 min, respectively.Moreover, it can be reused five times (M.Khan et al., 2021) Cango red is an azo dye that produces red in the water, hinders the transmission of sunlight, reduces the photosynthesis of aquatic life, and metabolizes human carcinogens from aqueous solutions.The adsorption of Congo red was reported by Khan and Al-Thabiti using trimetallic nanoparticles Fe-, Pd and Ir as a capping complex for chitosan.Their results presented an adsorption capacity of 93.4 mg/g through monolayer formation by physisorption.The adsorption was also confirmed theoretically with the Langmuir adsorption isotherm and pseudo-second-order kinetic model (Z.Khan & AL-Thabaiti, 2022).
Ali and coworkers also used chitosan carbon fiber loaded with monometallic and bimetallic Co, Ag, and Cu complexes to reduce toxic environmental pollutants such as para-nitrophenol, Congo red, and methyl orange dyes.Also, they tested the complex antibacterial activities against Escherichia coli (Z.Khan & AL-Thabaiti, 2022).
Abdulhameed and coworkers studied the efficiency of using Chitosan-ethylene glycol diglycidyl ether/TiO 2 nanoparticles as biosorbent for orange 16 dye from an aqueous solution.The composite adsorption followed the Freundlich and pseudo-second-order (PSO) kinetic models.The adsorption capacity of the composite was found to be 1407.4mg/g at 40°C (Z.Khan & AL-Thabaiti, 2022).

Microbes
Studying antimicrobial activities against different pathogens, such as bacteria and fungi, using chitosan biopolymer conjugated with various nanomaterials attracted many researchers.Bi et al. compared two different membranes by adding D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) to silicon oxide nanoparticles into Chitosan or Chitosan alone.α-tocopherol is a lipid-soluble antioxidant that protects the cell membrane against lipid peroxidation.Silicon dioxide nanoparticles are stable, nontoxic, and also safe food additives.And its addition to chitosan improves its mechanical strength, heat resistance, gas barrier, also antimicrobial effects.Adding (TPGS) to the complex changes their physical and chemical properties, such as crystallinity, moisture content, water vapour/oxygen permeability, tensile strength, and elongation upon distortion.Their studies show better TPGS/silicon dioxide nanoparticles/chitosan membrane properties than TPGS/chitosan.This membrane also showed enhanced free radical capture and oxidative stability, so it is a good antioxidant and enhances antimicrobial activity against four different food pathogens.This membrane can be used as a protective food-packing protecting layer (Z.Khan & AL-Thabaiti, 2022).Kumar et al. introduced a hydrogel composed of polyvinyl alcohol (PVA)/chitosan/silver nanoparticles.This hydrogel shows good antioxidant activity and enhanced antibacterial activity against gram-positive and gram-negative bacteria.The hydrogel can be used as an alternative to the present wound dressing to improve its antibacterial activity, low water content, and weak mechanical strength (Z.Khan & AL-Thabaiti, 2022).
Mallakpour and Abbasi used silver nanoparticles and silicon oxide nanoparticles embedded into a matrix of chitosan and tragacanth gum (polysaccharide biopolymers) to increase the growth of hydroxyapatite for bone regeneration.Additionally, they studied its antibacterial activity against gram-positive and gram-negative bacteria.Their synthesized nanocomposite showed a high antibacterial inhibition (Mallakpour & Abbasi, 2020).
Fernández et al. developed a hybrid biodegradable packing film with a thickness of 25 nm and a diameter ranging from 5 to 15 cm.This film consists of chitosan/azopolymer and silver nanoparticles prepared by solvent casting technique.The crafted film showed enhanced mechanical properties, induced birefringence properties, and broad antimicrobial activity (Fernández et al., 2020).

Discussion
Chitosan is a very important biopolymer with an active and rich surface chemistry.Many researchers reported its use with different nanoparticles, such as silver, gold, copper, titanium, ferric oxides, and carbon-based nanomaterials for water monitoring and purification from various chemical pollutants such as heavy metals.It is used for the adsorption of different dyes and in the form of composites or films against pathogenic microbes.Herein, we introduced a minireview to highlight this relevant and growing topic.Table 1 and Figure 3 summarize the topic.

Conclusion
Environmental and water pollutants increase every day.The increase in population and industry is the leading cause of this.Water is essential for our life, and the need to have clean water from different pollutants such as heavy metals, dyes, and organic pollutants is of great importance.Also, protecting humans from pathogenic microorganisms is crucial as it causes severe health problems that sometimes reach epidemic levels.The development of water remediation systems and environmental monitoring and purification is a growing field of study.Here, we focus on using chitosan-based nano-complexes for water and environment purifications.Chitosan is a surfaceactive, biocompatible, and eco-friendly biopolymer.It can form composites with different nanoparticles due to its reach surface chemistry.Figure 1 and Table 1 summarizes the review topics to use chitosan nano-complex for water remediation from heavy metals such as Cr (VI), Cs(I), Sb (III), Ferric (III), Fluoride, Cd (II), and PO 4 −3 , also get rid of dangerous dyes as methylene blue, ponceau, acid orange, and Rhodamine.Active nanomaterials based on chitosan to kill gram-positive and gram-negative bacteria and hazardous fungi are also reported.

Figure
Figure 1.The yearly number of publications on water treatment topic based of the statistics from Clarivate Web of Science TM .

Figure 3 .
Figure 3. Chitosan based nanocomplexes for water and environmental purifications.