Harmful algal blooms (HABs) are natural phenomenon that threatens public health, tourism, fisheries and ecosystems. Silica in its natural form is unable to mitigate HABs effectively and frequently modified with chitosan. In this study, the influence of crosslinking and swelling properties of rice husk ash silica/chitosan film reinforced with (3-glycidyloxypropyl) trimethoxysilane (GPTEOS) and glycerol (Gly) in capturing HABs cell, Alexandrium minutum was thoroughly investigated. The XRD analysis indicated that crosslinking had caused part of the chitosan’s crystalline network to become amorphous. The FTIR analysis showed that the chitosan, silica, glycerol and GPTEOS were crosslinked via a condensation reaction. The crosslinking was higher in the film containing GPTEOS (CHT/SiO2/GPTEOS) due to the condensation reaction between the GPTEOS epoxy group and the amine of chitosan in addition to the condensation of silanol and hydroxyl group of chitosan. As a result, the swelling of CHT/SiO2/GPTEOS was lower compared to Gly-containing film (CHT/SiO2/Gly). The RE value was 26.57 ± 10.81% using CHT/SiO2/Gly and 50.06 ± 11.90% using CHT/SiO2/GPTEOS. Based on the swelling and the RE trends, it is concluded that the initially trapped algae could have been released back into the environment when the films swelled. This study shows that crosslinking is important trapping the algae. The SEM and digital microscopic images of the used films revealed the presence of algae cells on the surface of the films. The films could be easily separated from the algae culture without sedimentation. The films also showed good biodegradability as all the films were fully degraded within 30 days of burial.
Research Article
Investigation on the influence of crosslinking and swelling properties of modified silica-chitosan films for the controlled removal of Alexandrium minutum
https://doi.org/10.21203/rs.3.rs-2737934/v1
This work is licensed under a CC BY 4.0 License
Version 1
posted
You are reading this latest preprint version
silica
Alexandrium minutum species
chitosan
glycerol
(3-glycidyloxypropyl) trimethoxysilane harmful algal bloom
Proliferations of toxic and nontoxic microalgal groups (e.g. diatoms, dinoflagellates, raphidophytes, haptophytes, pelagophytes, cryptophytes) and a few macroalgal species of green or brown algae can give rise to an aquatic phenomenon known as harmful algal blooms (HABs) [1–4]. A single occasion of HABs can seriously affect public health, tourism, fisheries and ecosystems [5,6]. Humans and animals are exposed to the biotoxins of the toxin-producing algae by consuming contaminated seafood and water activities such as swimming and inhaling droplets containing the biotoxin from the air. The non-toxic algae species may cause water discolouration and harm marine species through de-oxygenation of seawater, production of allelochemicals and mucus, or physical damage by spines or barbed setae [7–9]. The occurrence of HABs is attributed to eutrophication, climate change, transport and exchange of ballast water, and the development of the mariculture industry [10]. However, Hallegraaffe et al. [11] have a different opinion based on the outcome of their study. They reported that the increasing global trend of HABs occurrence is not due to these factors but due to rapid monitoring of HABs occurrence. Regardless, considering the HABs threats, actions to reduce its occurrence and impact needs to be taken. The term referring to the action taken to manage the existing or ongoing bloom and take steps to reduce the impact is known as mitigation [12]. Mitigation of HABs can be done through biological approach, physical approach, and chemical-physical approach [13]. Among these approaches, physical approach using mitigating agents have been found to be the most feasible method to mitigate HABs in the lab and field.
The suitability of materials to be used as HABs mitigating agents depends on the materials structure, particle size, effective interaction radius and surface charge [14, 15]. The mitigation agents must have a higher positive charge to attract and capture the negatively charged algae cell. The repulsive forces between the materials and algae cells will reduce the flocculation efficiencies [15]. The use of natural clays as a HABs mitigating agent was first introduced i1970s1970’s in the coastal water of Kagoshima, Japan. However, the flocculation ability of the natural clays was very low and required in a large amount. To enhance the electrostatic attraction between the mitigating agent and the algae cells, various organic and inorganic modifiers have been used.
Polyaluminium chloride (PAC) is an effective flocculant to flocculate and remove suspended particles from water bodies. Reports have shown that modifying clays with PAC increased the surface charge from negative to positive and enhanced the clays' flocculation efficiency. However, this effect is noted to be temporary. The algae cells were observed to escape from the floc and continue reproducing [16,17]. Jiang et al. [19], investigated the effect of adding NaCl on the settling rate of PAC modified kaolin. The addition of NaCl increased the ionic strength leading towards forming larger flocs, increasing the settling rate. The settling rate of modified clay improved by two-fold and the removal efficiency of the HAB cells (Nannochloris, Gyrodinium and Heterosigma) increased by 7–28%.
Alshahri et al. reported that the addition of low doses (0.01 mg/L, 0.10 mg/L, and 1.00 mg/L) of liquid ferrate (58% yield) to kaolin or montmorillonite clays removed 71-84% of algal cells (species not specified) in addition to improving the quality of the water [20]. The removal efficiency is attributed to the synergistic processes of charge neutralization and netting-bridging. Ren et al. [21] reported that PAC modified kaolin successfully inhibited more than 90% of Phaeocystis globose. The group has concluded that the modified clay may have damaged the cell walls upon collision, in addition, to be able to change the environment to suppress the growth of Phaeocystis globose.
Silica is another abundantly available natural materials that has the potential to be developed to mitigate HABs. However, compared to clays only a handful of research on the application in HABs mitigation has been carried out despite its potential.
Pan et al. [22] reported that beach sand modified with chitosan and PAC achieved 80% removal efficiency for Amphidinium carterae Hulburt and Chlorella sp. in 3 min using 120 mg L-1 sand modified with 10 mg L-1 PAC and 10 mg L-1 chitosan. They concluded that chitosan acted as a bridge linking together all the smaller flocs formed by the PAC to form larger and denser flocs for faster sedimentation. In addition, the chitosan also function as a trap to prevent the cells from escaping from the flocs. The sand acted as ballast for sedimentation.
Chen and Pan [23] showed that xanthan could trap the algae cells similar to chitosan and the efficiency enhanced in the presence of calcium hydroxide. The removal efficiency of Amphidinium carterae Hulburt culture increased to 83–89% within 30 min using 300 mg L−1 clays, soils, or sands modified with 20 mg L−1 xanthan and 100 mg L−1 calcium hydroxide. Whereas, only 55% of removal was achieved when xanthan was use alone. The addition of Ca(OH)2 decreased the repulsive interaction between anionic xanthan and negatively charged algal cells.
Jin et al. [24] investigated the potential of bicomponent modified soil using amphoteric starch (AS) and poly-aluminium chloride (PAC) for the mitigation of Microcystis aeruginosa and marine Chlorella sp. The removal efficiency was contributed to 99.9% removal efficiency of in fresh and saline waters, and Chlorella sp. in marine water.
Diaz et al. [25] developed a novel silica-based antimicrobial nanofilm using a composite of silica-modified quaternary ammonium compounds, didecyldimethylammonium chloride solution (Fixed-Quat) applied to a fiberglass mesh for the mitigation of Microcystis aeruginosa. More than 99% of Microcystis aeruginosa was removed after 10 hr of exposure. The inhibition is attributed to the electrostatic attraction between the negatively charged algae and the alkyl chain of the didecyldimethylammonium chloride solution which can cause the disruption of the cytoplasmatic membrane hence, killing the algae.
Sedimentation of mitigating agents especially materials that are not native to the area such as clays and the application of inorganic modifiers could possibly raise concern on the stability of the aquatic ecosystems in the long run. As an alternative, the clays or sand can be attached on the chitosan film. The function of the chitosan film will be as a trap for the algae cells and improve the charge of the of the clay or silica and to enhance the electrostatic charge between the film and the algae cells. The advantage of the composite films over the typical clays and sands is that the film can re recollected for disposal after the HABs season ends
However, chitosan film tends to be hard and fragile. To get around this restriction, modifiers that functions as plasticizer is postulated to be able to enhance the mechanical and physical characteristics of chitosan film. Plasticizers are known to be effective in lowering the intermolecular forces between polymer chains and increasing their mobility, thereby improving mechanical properties [26,27].
The goal of this work is to prepare silica/chitosan film reinforced with (3-glycidyloxypropyl) trimethoxysilane (GPTEOS) and glycerol (Gly) film for the mitigation of toxic algae cells, Alexandrium minutum (A. minutum). Instead of harvesting the sand, the silica will be prepared from rice husk which is an agricultural waste that is often discarded as waste by open burning. The rice husk contains 28% with almost 90% amorphous silica content that is suitable to be modified with chitosan [28]. The biodegradability of the films were also investigated.
Materials
The rice husk was collected from a rice mill in Penang, Malaysia. Other chemicals such as hydrochloric acid (Sigma-Aldrich, 37% United States), chitosan powder (Sigma Aldrich, medium molecular weight, product id: 448877, Unites states), nitric acid (Qrec, 65%, Malaysia), sodium hydroxide pellets (Qrec, 99% Malaysia), glacial acetic acid (Qrec, 100%, Malaysia), glycerol (Qrec, 99.5%, Malaysia) and (3-glycidyloxypropyl) trimethoxysilane (GPTEOS, Sigma-Aldrich, 98%, United States) were used without further purification. Filtered fresh water was used for the mitigation studies and was supplied by Fisheries Research Institute (FRI), Batu Maung, Penang, Malaysia.
Preparation of rice husk ash
The rice hush ash (RHA) was prepared according to the procedure reported by Adam et al. [28]. The rice husk (RH) was thoroughly cleansed with plenty of distilled water to get rid of the dirt, and it then dried for two days at room temperature. To remove the metallic impurities, the cleaned RH (30 g) was agitated for 24 hours at room temperature in 750 ml of prepared 1.0 M HNO3. Until the filtrate was colorless, the RH that had been treated with acid was washed with distilled water. The RH was then dried in a 100 oC for 24 h and calcined for 6 h at 600 oC in a muffle furnace to produce white colored RHA.
Preparation of sodium silicate solution
Sodium silicate solution was prepared according to the method reported by Sumarni et al. [28] with some modifications. The RHA (3 g) was dissolved in 350 mL of 1.0 M NaOH and stirred at 70 oC for 6 h. The semi-dried product was subjected to calcination for 30 min at 600 oC to obtain sodium silicate powder. A clear sodium silicate solution was obtained by dissolving 1.71 g of the powder in 200 mL of distilled water.
Synthesis of hybrid silica/chitosan films
The hybrid films were prepared using the method reported by Liu et al. [29] with some modifications. Chitosan solution (2% w/v) was prepared by dissolving chitosan powder (2 g) in 100 mL, 1% v/v, acetic acid solution. The solution was stirred for 4 h at 50 oC followed by centrifugation at 4000 rpm for 15 min and filtered to remove any undissolved chitosan powder. Glycerol or (3-(glycidyloxypropyl)trimethoxysilane) (3 ml, 1% v/v) was added to the filtered chitosan solution and stirred for 2 h to form a homogeneous solution and to reduce bubbles formation. The film-forming solution was then poured into a square-shaped Teflon mold and dried in the oven for 21 h at 50 oC. A sodium hydroxide solution (NaOH) solution (2% w/v) was prepared by dissolving 10.0 g NaOH pellets in 500 mL distilled water. The dried film was soaked in 2% w/v NaOH solution for a minute and rinsed with distilled water to neutralise it. The film was then dried at room temperature for 24 h and kept in the desiccator for further use. The hybrid chitosan/silica/glycerol film, and hybrid chitosan/silica/(3-(glycidyloxypropyl)trimethoxysilane) film were labelled as CHT/SiO2/Gly and CHT/SiO2/GPTEOS, respectively. The digital images of the films are shown in Fig. S1.
Characterizations
The surface topology of the films was analysed using Scanning electron microscope (SEM Leica Cambridge S360). Bruker-D8 Advance Powder X-ray diffraction (XRD) was used to determine the films' crystalline phases and degree of crystallinity at 2θ angle of 5o to 50o. The films' swelling index (SI) was conducted by submerging the pre-weighed dry films into 100 mL of seawater for 24 h at room temperature. After 24 h, the swollen films were removed, wiped with filter paper to remove excess water and weighed. The SI was calculated using Equation (1) as reported by Liu et al. [29] and Sabzevari et al. [30]. Three different films were used for the measurement to obtain the average swelling index. The seawater pH before and after film immersion was recorded using a pH meter (Model Hanna edgepH).
where Wf is the weight of the swollen film after 24 h and Wi is the weight of dry film before being submerged.
The film's wettability or water contact angle (CA) was tested via the static CA using a goniometer (Rame’-Hart Instrument Co., United States) based on the sessile drop method. Deionised water (4 µL) was dropped using a microsyringe onto the smooth surface of the film at room temperature. Then, a microscope was used to capture the micrographs. This step was repeated for five different spots of the films to calculate the average CA.
Mitigation studies
The mitigation studies were conducted at Fisheries Research Institute (FRI), Batu Maung, Penang, Malaysia. Alexandrium minutum culture in the mid to late exponential growth phase was used as the source of HABs. The experiment was conducted in 250 mL beakers containing 150 mL of cell cultures (20,000 cells/mL). Each replicates’ culture’s pH and temperature were recorded every day using pH meter (Hanna edgepH).
In a typical mitigation experiment, the films were tied to a rod and hanged vertically with three-quarters of the film was immersed into the cell cultures for the moving cells to be adsorbed. The experimental set up is shown in Fig. S2. The beakers were placed on the table in a static condition. Approximately 1 mL of samples from 2 cm below the surface were collected and preserved with one drop of Lugol’s solution at each specific time interval. The removal efficiency was determined for 72 h. The preserved cells were counted using the Sedgwick-rafter counter under a light microscope (Leica CME) at 10x magnification. The effects and changes of the cells on the surface of the films were also observed under the Digital microscope (Keyence VHX E-100). Removal efficiency rate (RE) was calculated using Equation (2) [32]. All the RE data were expressed as the mean±standard deviation (S.D).
Biodegradation of films in the soil
The biodegradability of the used films was analysed by burying in the soil. In a typical experiment, natural soil was used and filled in a 20 cm deep plastic container. The films were buried at a depth of 15 cm for a total of 30 days, and the containers were placed on an open area exposed to the elements of surrounding nature. The films were taken out every 7 days, wiped with the filter paper to remove the excess soil and dried at 60 oC for 6 h. The weight loss of the films at different burial time was recorded. The physical changes in the films were captured. The percentage of degradation was calculated using the following Equation (3).
where Wi and Wf are the initial weight and final weight of the film at different burial times, respectively.
X-ray diffraction (XRD)
Figure 1 shows the diffractograms of the films. Three diffraction peaks were observed at 2θ= 10.1°, 20.1° and 21.8°, corresponding to the crystallographic planes (002), (101) and (220) of chitosan, respectively [31, 32].The XRD peaks at 2θ= 10.1° is attributed to the hydrated crystallite structure of chitosan due to the integration of water molecules in the crystal lattice whereas the peak at 2θ= 20.1° is associated with the regular chitosan crystal lattice. The diffraction peak at 2θ= 22° corresponds to the amorphous structure of the chitosan. The appearance of diffraction peak related to the amorphous nature of chitosan indicate that the crosslinking of glycerol and GPTEOS to the chitosan polymeric network are strong enough to change the crystal structure of the chitosan [33, 34, 37. The XRD diffraction peak of amorphous silica can be observed at 2θ= 22° as well [38].
Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR)
The ATR-FTIR spectra of the films are shown in Fig. 2. The peak at 1016 cm-1 corresponds to the symmetric stretching of the C-O-C bond. The peak at 1075 cm-1 is attributed to the skeletal vibration of C-O and is usually assigned as the fingerprint peak for the chitosan structure. The IR peak is at 1554 cm-1 is attributed to the N-H bending vibration and C-N stretching vibration in the region of amide II [30, 39], whereas the second peak at 1645 cm-1 is associated with the C-O stretching of amide I [39, 40]. The peak at 1384 cm-1 and a shoulder at 1317 cm-1 correspond to asymmetric С-О-С stretching vibrations and С-О stretching vibration of СН-ОН. The asymmetric and symmetric stretching vibrations of NH bond is reflected though the presence of IR band around 3000-3500 cm-1 [39]. The peak at the region can also be attributed to the stretching vibration of SiO–H bond and adsorbed water (HO-H) on the silica surface [41]. The band appears to be more intense and broader in CH/SiO2/Gly indicating an abundance in OH concentration compared to CHT/SiO2/GPTEOS. This observation could also indicate that crosslinking in CHT/SiO2/GPTEOS took place through silanol groups. The peak around 1000-1100 cm-1 can also be associated with the Si-O-Si bond [42]. In the FTIR spectrum of CHT/SiO2/Gly , the bending of the C-O-H can be observed in the region at 1416 cm-1 whereas the peak associated to C-O stretching of the primary alcohol is visible at 1162 cm-1. The peak at 1362 cm-1 is attributed to C-H vibration of the glycerol [41].
The crosslinking between chitosan and silica can take place when the silanol group of the silica reacted with the hydroxyl groups of the chitosan through condensation reaction to form Si-O-C bond (indicated in red line). The IR peak related to Si-O-C bond is normally can be seen around 1252 cm-1 [42]. However, it is difficult to distinguish due to the overlapping of different band structures. The schematic representation of the crosslinking is shown in Scheme 1.
Similarly, the glycerol can react with the silanol group of the silica and the hydroxyl group of the chitosan group through condensation to form the framework of CHT/SiO2/Gly. The reaction is shown in Scheme 2.
The FTIR peaks of epoxy and ethoxy which could be observed generally around 1074 cm-1 and 2852 cm-1, respectively could not be observed in the FTIR spectrum of CHT/SiO2/GPTEOS. The disappearance indicate that the crosslinking has taken place through the components. The GPTEOS can be hydrolysed by water to organosilicon compound (A) and the removal of ethoxy group as C2H5OH. The reaction scheme is shown in Scheme 3 (a).
The compound can react with the hydroxyl group of the silanol through condensation reaction to form organosilicon compound (B). The epoxy ring of (B) can cleave and react with the amine of the chitosan to form the CHT/SiO2/GPTEOS as shown in Scheme 3 (b), in addition to the reaction between the amine and epoxide, silanol groups of silica can also react with the remaining hydroxy of the chitosan. The peaks associated to the OH and NH2 at 2900 cm-1 reduced significantly compared to other composite films indicating utilization of these functional groups in the formation of the composite film.
Scanning Electron Microscopy -Energy Dispersive X-Ray (SEM-EDX)
Figure 3 shows the SEM images of CHT/SiO2/Gly and CHT/SiO2/GPTEOS. The surface of CHT/SiO2/Gly (Fig. 3(a)) and CHT/SiO2/GPTEOS (Fig. 3(b)) appears to be highly uneven. The addition of Gly and GPTEOS among others can improve the flexibility and extendibility of a polymer. These properties are obtained by weakening or even breaking the intermolecular bonds. The weakening of the bonds could possibly can the arrangements of the polymeric chain and cause the film to shrink during the drying process. The cross section of CHT/SiO2/Gly (Fig. 3(c)) appears to have microcracks and voids. The FTIR analysis of CHT/SiO2/Gly indicate the presence of abundant amount of OH bonds which can form hydrogen bonding within the polymeric chain. The hydrogen bonding can induce anti-plasticizing effect to form tighter polymeric network. As a result of this effect, tighter polymeric network can cause micro-cracking on the surface [43]. The voids and microcracks can be seen in the cross-section image of CHT/SiO2/Gly. The microcracks and void were not prominent in the cross section of CHT/SiO2/GPTEOS (Fig. 3(d)) due to the lack of OH bond to induce the anti-plasticizing effect but the film has a dense structure.
Wettability test
Wettability test measures the level of wetting when solid and liquid phases interact with each other. The wettability of CHT/SiO2/Gly and CHT/SiO2/GPTEOS is determined by measuring the contact angle between the films and water droplet. Greater wettability is signified if the contact angle is ≤ 90° whereas contact angle ≥ 90°indicate lower wettability [44]. As shown in Fig. 4, CHT/SiO2/Gly (58.28 o ± 0.03º) has lower contact angle compared to CHT/SiO2/GPTEOS (84.92 ± 0.05º). This observation can be explained based on FTIR analysis. The analysis showed that CH/SiO2/Gly has higher amount of OH group which allows water to form hydrogen bond with the film’s surface. The contact angle CHT/SiO2/GPTEOS is higher due to the lack of OH bond to form hydrogen bond with the water molecules.
Film thickness and swelling index of the films
Blending chitosan matrix with other component often increases the film’s thickness. However, in this research, the thickness of the films did not change significantly as shown in Table 1. The presence of silicate species with the chitosan framework causes the tighter binding and the structure of the film becomes more compact [45]. In addition, due to the glycerol hydrodynamic radius [46], the glycerol molecules tend to increase the spacing between the chitosan macromolecules located in each layer instead of separating them. Plasticiser molecules surrounding the polymer molecules interact by hydrogen bonds at specific sites (-OH, -NH2), suppressing the film from having greater thickness. The crosslinking in CHT/SiO2/GPTEOS is higher causing the layers of chitosan macromolecules to be closer,
The swelling index of the films is presented in Table 1 as well. It can be seen that the CHT/SiO2/Gly has a higher swelling index compared to CHT/SiO2/GPTEOS. This is possible since the film has plenty of functional groups such -OH and -NH2 which can form hydrogen bonds with water molecules [47]. These functional groups increase the film's swelling [48,49]. The GPTEOS is a well-known hydrophobic organosilane. Hence, it is expected for the swelling index to be lower than the rest of the films.
Table 1 The obtained film thickness, density and swelling index of the film.
|
Film sample |
Thickness (mm) |
Swelling index (%) |
|
CHT/SiO2/Gly |
0.366 ± 0.04 |
60.03 ± 1.09 |
|
CHT/SiO2/GPTEOS |
0.367 ± 0.02 |
45.53 ± 1.17 |
*The values were expressed in mean± standard deviation with significant difference (p<0.05)
Point of zero charge (PZC) refers to the pH values at which the surface charge components become equal to zero under given conditions of temperature, applied pressure, and aqueous solution composition [50]. However this does not mean the surface is free from any charges, it means the surface positive charge is equal to the negative charge [51]. The pHpzc of CHT/SiO2/Gly and CHT/SiO2/GPTEOS was calculated to be 4.39 and 4.27, respectively (Fig. 5).
Mitigation of Alexandrium minutum
The removal efficiency (RE) of the film is shown in Fig. 6. The RE values were observed to fluctuate for the first three hours (RE= 18.1 ± 9.81-25.9 ± 10.16 %) and during this period the films were observed to start to swell. It is postulated that during the swelling stage, the algae cells that were initially trapped within the framework of the films escaped. The CHT/SiO2/GPTEOS recorded least changes at this period due to its low swelling index. The RE value started to increase rapidly from the 10th h to 20th h, then started to drop and fluctuate until the end of the experiment. The removal of Alexandium minutum at 72 h was 26.57 ± 10.81% using CHT/SiO2/Gly and 50.06 ± 11.90% using CHT/SiO2/GPTEOS. The statistical analysis revealed significant differences between each film tested (p<0.05).
The pH of culture increased slightly from 6.61 to 6.69 in the presence of the films. Since the pH is within the normal range for aquatic animals, it indicates that the algae died from the attachment on the films, not because of the change in pH.
The RE value of CHT/SiO2/Gly and CHT/SiO2/GPTEOS was noticed to be lower compared with published silica- based HABs mitigation agents as shown in Table 2. Only a few publications can be found on regarding the utilization of silica as HABs mitigating agent. Two factors can be attributed to this observation. 1) The films continued to swell throughout the mitigation studies. Hence, the initially absorbed algae cells were able to escape. 2) The pHPZC of the films is lower compared to pH of the culture. Hence, the surface of the films will be negatively charged. Since the algae is negatively charged as well, the electrostatic repulsion will overcome the electrostatic attraction. As a result, the number of collisions between the algae and the films for maximum removal will be reduced. This conditions can lead to lower RE value. The capture and release mechanism of the algae cells by the CHT/SiO2/Gly and CHT/SiO2/GPTEOS is simplified in Fig. 7.
Table 2 Removal efficiency of different types of algae using silica-based mitigating agents.
|
Mitigating agent |
HAB species |
Removal Efficiency |
Reference |
|
Silica-modified QAC (Fixed-Quat) and applied to a fiberglass mesh |
Microcystis aeruginosa |
99% inactivation after 10 hr of exposure. |
[24] |
|
Local beach sand or silica sand modified with chitosan and polyaluminum chloride (PAC). |
Amphidinium carterae Hulburt and Chlorella sp. |
80% within 3 min of exposure |
[21] |
|
Xanthane and calcium ydroxide modified clays, soils, and sands) |
Amphidinium carterae |
83–89% within 30 min of exposure |
[22] |
|
Modified soil using amphoteric starch (AS) and poly-aluminium chloride (PAC) |
Microcystis aeruginosa and marine Chlorella sp.
|
99.9% removal efficiency within 5-250 min of exposure. |
[23] |
Digital microscopy analysis of the films after mitigation
The used films were analysed with digital microscopy. The digital microscopic images showed that the algae cells attached to the CHT/SiO2/Gly ruptured (Fig 8(a)), whereas the algae cells on the CHT/SiO2/GPTEOS film remained intact. Since NH2 group of chitosan is preserved in CH/SiO2/ Gly, the positively charged amine groups in the chitosan structure could induce stress to the algal cells and promotes cell rupturing [21, 52]. Whereas in CHT/SiO2/GPTEOS film, most of the NH2 of chitosan is used up during the crosslinking process, hence further reducing the electrostatic charge and prevented the algae cells from rupturing.
SEM analysis of the films after mitigation
The used films were subjected to SEM analysis to observe any changes on their morphology. As can be seen in Fig. 9(a), a lump of mass possibly the ruptured algae cells can be observed on the surface of CHT/SiO2/Gly whereas on the surface of CH/SiO2/GPTEOS, irregularly rectangle shaped particles can be seen. Algae cells has various type of functional groups such as -OH and NH2 which can react with the films’ framework through hydrogen bonding [53]. During the drying process, the structure of the algae could have changed due to the removal of water and bonding. Further investigation is being carried out to understand the cause of the morphological changes.
Biodegradation of the used films in the soil
Chitosan has been used extensively due to its biocompatibility and biodegradability properties. The biodegradable behaviour of the used films in the soil were observed for one month by taking the pictures and recording the weight loss. The physical changes of the buried films were shown using the red circle in Fig. 10. The films became brittle and started to lose their shape and break into pieces after being buried for 7 days. The films were degraded completely at the end of 28th day where no traces of films were found in the soil. All the films exhibit good biodegradable properties as it is totally degraded after being buried for 30 days. The rapid degradation and faster disappearance by the films in the soil adds an advantage to dispose of the used films safely without creating pollution to the aquatic environment.
The mitigation ability of silica/chitosan film reinforced with (3-glycidyloxypropyl) trimethoxysilane (GPTEOS) and glycerol (Gly) in capturing HABs cell, Alexandrium minutum is influenced by the degree of crosslinking and swelling properties of the film. The film containing GPTEOS (CHT/SiO2/GPTEOS) was observed to have higher degree of crosslinking compared to the film containing Gly (CHT/SiO2/Gly). The crosslinking between the GPTEOS is proposed to take place through condensation reaction between the epoxy group and the amine group of the chitosan in addition to the reaction between the hydroxyl group of the chitosan and the silanol groups. Higher degree of crosslinking reduced the ability of the film to swell. As a result, the removal efficiency (RE) value of CHT/SiO2/GPTEOS was 50.06 ± 11.90% which is higher compared to CHT/SiO2/Gly. The lower RE value of CHT/SiO2/Gly is due to its lower crosslinking degree which allows the film to swell at greater extend hence causing the trapped algae to escape back to the medium. The film was able to be separated and degraded within 30 days in soil.
Author Contribution
AI & DHYY: Conceptualization, Fund acquisition, Supervision, Writing-review & editing, Project administration and Resources. NMN & RMR: Conceptualization & Supervision. LDW, NHI & NJ: Performed the major experiments, Data curation, Formal analysis, Writing – original draft. All authors reviewed the results and approved the final version of the manuscript.
Acknowledgements
The authors would like to thank Universiti Sains Malaysia for funding this research through Research University Grant (RUI) (1001/PKIMIA/8011083) and also Fisheries Research Institute (FRI), Batu Maung, Malaysia for granting the permission to use their facilities to conduct mitigation studies. The authors also acknowledge the facilities, the scientific and technical assistance of the Integrated Laboratory of Bioproducts, National Research and Innovation Agency (BRIN).
Conflict of Interest
The authors declare no conflict of interest.
- Smayda TJ (1997) Harmful algal blooms: Their ecophysiology and general relevance to phytoplankton blooms in the sea. Limnol Oceanogr. 42(5part2):1137-1153. doi:10.4319/lo.1997.42.5_part_2.1137
- Hoagland P, Anderson DM, Kaoru Y, White AW (2002) The economic effects of harmful algal blooms in the United States: Estimates, assessment issues, and information needs. Estuaries. 25(4):819-837. doi:10.1007/BF02804908
- Smetacek V, Zingone A (2013) Green and golden seaweed tides on the rise. Nature. 504(7478):84-88. doi:10.1038/nature12860
- Anderson CR, Moore SK, Tomlinson MC, Silke J, Cusack CK (2015) Living with Harmful Algal Blooms in a Changing World. In: Coastal and Marine Hazards, Risks, and Disasters. Elsevier 495-561. doi:10.1016/B978-0-12-396483-0.00017-0
- Bresnan E, Arévalo F, Belin C, et al. (2021) Diversity and regional distribution of harmful algal events along the Atlantic margin of Europe. Harmful Algae. 102:101976. doi:10.1016/j.hal.2021.101976
- Anderson DM, Fensin E, Gobler CJ, et al. (2021) Marine harmful algal blooms (HABs) in the United States: History, current status and future trends. Harmful Algae. 102:101975. doi:10.1016/j.hal.2021.101975
- Anderson DM (2019) Harmful Algal Blooms. In: Encyclopedia of Ocean Sciences. Elsevier; 309-321. doi:10.1016/B978-0-12-409548-9.11468-X
- Li XY, Yu RC, Richardson AJ, et al. (2023) Marked shifts of harmful algal blooms in the Bohai Sea linked with combined impacts of environmental changes. Harmful Algae. 121:102370. doi:10.1016/j.hal.2022.102370
- Xiao Z, Tan AX, Xu V, Jun YS, Tang YJ (2022) Mineral-hydrogel composites for mitigating harmful algal bloom and supplying phosphorous for photo-biorefineries. Sci Total Environ. 847:157533. doi:10.1016/j.scitotenv.2022.157533
- Glibert PM (2020) Harmful algae at the complex nexus of eutrophication and climate change. Harmful Algae. 91:101583. doi:10.1016/j.hal.2019.03.001
- Hallegraeff GM, Anderson DM, Belin C, et al. (2021) Perceived global increase in algal blooms is attributable to intensified monitoring and emerging bloom impacts. Commun Earth Environ. 2(1):117. doi:10.1038/s43247-021-00178-8
- Anderson DM (2009) Approaches to monitoring, control and management of harmful algal blooms (HABs). Ocean Coast Manag. 52(7):342-347. doi:10.1016/j.ocecoaman.2009.04.006
- Ibrahim NH, Iqbal A, Mohammad-Noor N, et al. (2022) A Review on The Biological, Physical and Chemical Mitigation of Harmful Algal Bloom. Squalen Bull Mar Fish Postharvest Biotechnol. 17(2):95-110. doi:10.15578/squalen.633
- Rosa M, Ward JE, Holohan BA, Shumway SE, Wikfors GH (2017)Physicochemical surface properties of microalgae and their combined effects on particle selection by suspension-feeding bivalve molluscs. J Exp Mar Biol Ecol. 486:59-68. doi:10.1016/j.jembe.2016.09.007
- Yu Z, Sun X (1994) Effects of e-e Interaction on the CDW of MX Complex. Chin Phys Lett. 11(2):105-108. doi:10.1088/0256-307X/11/2/012
- Zhi-ming Y, Jing-zhong Z, Xi-nian M (1994) Application of clays to removal of red tide organisms I. Coagulation of red tide organisms with clays. Chin J Oceanol Limnol. 12(3):193-200. doi:10.1007/BF02845163
- Sengco M, Li A, Tugend K, Kulis D, Anderson D (2001) Removal of red- and brown-tide cells using clay flocculation. I. Laboratory culture experiments with Gymnodinium breve and Aureococcus anophagefferens. Mar Ecol Prog Ser. 210:41-53. doi:10.3354/meps210041
- Sun XX, Lee YJ, Choi JK, Kim EK (2004) Synergistic effect of sophorolipid and loess combination in harmful algal blooms mitigation. Mar Pollut Bull. 48(9-10):863-872. doi:10.1016/j.marpolbul.2003.11.002
- Jiang W, Yu Z, Cao X, et al. (2021)Effects of soluble organics on the settling rate of modified clay and development of improved clay formulations for harmful algal bloom control. Environ Pollut. 289:117964. doi:10.1016/j.envpol.2021.117964
- Alshahri AH, Fortunato L, Ghaffour N, Leiknes T (2021) Controlling harmful algal blooms (HABs) by coagulation-flocculation-sedimentation using liquid ferrate and clay. Chemosphere. 274:129676. doi:10.1016/j.chemosphere.2021.129676
- Ren X, Yu Z, Qiu L, Cao X, Song X (2021) Effects of Modified Clay on Phaeocystis globosa Growth and Colony Formation. Int J Environ Res Public Health. 18(19):10163. doi:10.3390/ijerph181910163
- Pan G, Chen J, Anderson DM (2011) Modified local sands for the mitigation of harmful algal blooms. Harmful Algae. 10(4):381-387. doi:10.1016/j.hal.2011.01.003
- Chen J, Pan G (2012) Harmful algal blooms mitigation using clay/soil/sand modified with xanthan and calcium hydroxide. J Appl Phycol. 24(5):1183-1189. doi:10.1007/s10811-011-9751-7
- Jin X, Bi L, Lyu T, Chen J, Zhang H, Pan G (2019) Amphoteric starch-based bicomponent modified soil for mitigation of harmful algal blooms (HABs) with broad salinity tolerance: Flocculation, algal regrowth, and ecological safety. Water Res. 165:115005. doi:10.1016/j.watres.2019.115005
- Diaz D, Church J, Young M, et al. (2019) Silica-quaternary ammonium “Fixed-Quat” nanofilm coated fiberglass mesh for water disinfection and harmful algal blooms control. J Environ Sci. 82:213-224. doi:10.1016/j.jes.2019.03.011
- Yu J, Xu S, Goksen G, Yi C, Shao P (2023) Chitosan films plasticized with choline-based deep eutectic solvents: UV shielding, antioxidant, and antibacterial properties. Food Hydrocoll. 135:108196. doi:10.1016/j.foodhyd.2022.108196
- Syaubari, Abubakar, Asnawi TM, Zaki M, Khadafi M, Harmanita I (2022) Synthesis and characterization of biodegradable plastic from watermelon rind starch and chitosan by using glycerol as plasticizer. Mater Today Proc. 63:S501-S506. doi:10.1016/j.matpr.2022.04.535
- Adam F, Appaturi JN, Iqbal A (2012)The utilization of rice husk silica as a catalyst: Review and recent progress. Catal Today. 190(1):2-14. doi:10.1016/j.cattod.2012.04.056
- Sumarni W, Iswari RS, Marwoto P, Rahayu EF (2016) Physical characteristics of chitosan-silica composite of rice husk ash. IOP Conf Ser Mater Sci Eng. 107:012039. doi:10.1088/1757-899X/107/1/012039
- Liu Y, Cai Z, Sheng L, Ma M, Xu Q (2019) Influence of nanosilica on inner structure and performance of chitosan based films. Carbohydr Polym. 212:421-429. doi:10.1016/j.carbpol.2019.02.079
- Sabzevari M, Cree DE, Wilson LD (2019) Mechanical properties of graphene oxide-based composite layered-materials. Mater Chem Phys. 234:81-89. doi:10.1016/j.matchemphys.2019.05.091
- Kim ZH, Thanh NN, Yang JH, et al. (2016) Improving microalgae removal efficiency using chemically-processed clays. Biotechnol Bioprocess Eng. 21(6):787-793. doi:10.1007/s12257-016-0655-x
- Khan A, Khan RA, Salmieri S, et al. (2012) Mechanical and barrier properties of nanocrystalline cellulose reinforced chitosan based nanocomposite films. Carbohydr Polym. 90(4):1601-1608. doi:10.1016/j.carbpol.2012.07.037
- Argüelles-Monal W, Lizardi-Mendoza J, Fernández-Quiroz D, Recillas-Mota M, Montiel-Herrera M (2018) Chitosan Derivatives: Introducing New Functionalities with a Controlled Molecular Architecture for Innovative Materials. Polymers. 10(3):342. doi:10.3390/polym10030342
- Madian NG, Mohamed N (2020)Enhancement of the dynamic mechanical properties of chitosan thin films by crosslinking with greenly synthesized silver nanoparticles. J Mater Res Technol. 9(6):12970-12975. doi:10.1016/j.jmrt.2020.09.028
- Shehap AM, Nasr RA, Mahfouz MA, Ismail AM (2021) Preparation and characterizations of high doping chitosan/MMT nanocomposites films for removing iron from ground water. J Environ Chem Eng. 9(1):104700. doi:10.1016/j.jece.2020.104700
- Matei PM, Martín-Ramos P, Sánchez-Báscones M, et al. (2015) Synthesis of Chitosan Oligomers/Propolis/Silver Nanoparticles Composite Systems and Study of Their Activity against Diplodia seriata. Int J Polym Sci. 1-11. doi:10.1155/2015/864729
- Issa HK, Maleki A, Taherizadeh A, Zargaran A (2022) On the structure-properties relationship of amorphous and crystalline silica nanoparticles reinforced magnesium matrix nanocomposites. J Alloys Compd. 924:166605. doi:10.1016/j.jallcom.2022.166605
- Fernandes Queiroz M, Melo K, Sabry D, Sassaki G, Rocha H (2014) Does the Use of Chitosan Contribute to Oxalate Kidney Stone Formation? Mar Drugs. 13(1):141-158. doi:10.3390/md13010141
- Wan Y, Wu H, Yu A, Wen D (2006) Biodegradable Polylactide/Chitosan Blend Membranes. Biomacromolecules. 7(4):1362-1372. doi:10.1021/bm0600825
- Mujeeb Rahman P, Abdul Mujeeb VM, Muraleedharan K, Thomas SK (2018) Chitosan/nano ZnO composite films: Enhanced mechanical, antimicrobial and dielectric properties. Arab J Chem. 2018;11(1):120-127. doi:10.1016/j.arabjc.2016.09.008
- Ellerbrock R, Stein M, Schaller J (2022) Comparing amorphous silica, short-range-ordered silicates and silicic acid species by FTIR. Sci Rep. 12(1):11708. doi:10.1038/s41598-022-15882-4
- Gómez-Siurana A, Marcilla A, Beltrán M, Berenguer D, Martínez-Castellanos I, Menargues S (2013) TGA/FTIR study of tobacco and glycerol–tobacco mixtures. Thermochim Acta. 573:146-157. doi:10.1016/j.tca.2013.09.007
- Jung Sang Shin, Oh T (2006) Generation of Si-O-C bond without Si-CH3 bond in hybrid type SiOC Film. In: 2006 IEEE Nanotechnology Materials and Devices Conference. IEEE; 2006:462-463. doi:10.1109/NMDC.2006.4388817
- Liu H, Adhikari R, Guo Q, Adhikari B (2013) Preparation and characterization of glycerol plasticized (high-amylose) starch–chitosan films. J Food Eng. 116(2):588-597. doi:10.1016/j.jfoodeng.2012.12.037
- Sarkar M, Hasanuzzaman M, Gulshan F, Rashid A (2022) Surface, Mechanical and Shape Memory Properties of Biodegradable Polymers and Their Applications. In: Encyclopedia of Materials: Plastics and Polymers. Elsevier; 1092-1099. doi:10.1016/B978-0-12-820352-1.00050-X
- Yeh JT, Chen CL, Huang KS (2007) Synthesis and properties of chitosan/SiO2 hybrid materials. Mater Lett. 61(6):1292-1295. doi:10.1016/j.matlet.2006.07.016
- Quijadagarrido I, Iglesiasgonzalez V, Mazonarechederra J, Barralesrienda J (2007) The role played by the interactions of small molecules with chitosan and their transition temperatures. Glass-forming liquids: 1,2,3-Propantriol (glycerol). Carbohydr Polym. 68(1):173-186. doi:10.1016/j.carbpol.2006.07.025
- Clasen C, Wilhelms T, Kulicke WM (2006) Formation and Characterization of Chitosan Membranes. Biomacromolecules. 7(11):3210-3222. doi:10.1021/bm060486x
- Palla-Rubio B, Araújo-Gomes N, Fernández-Gutiérrez M, et al. (2019) Synthesis and characterization of silica-chitosan hybrid materials as antibacterial coatings for titanium implants. Carbohydr Polym. 203:331-341. doi:10.1016/j.carbpol.2018.09.064
- Huang L, Dai T, Xuan Y, Tegos GP, Hamblin MR (2011) Synergistic Combination of Chitosan Acetate with Nanoparticle Silver as a Topical Antimicrobial: Efficacy against Bacterial Burn Infections. Antimicrob Agents Chemother. 55(7):3432-3438. doi:10.1128/AAC.01803-10
- Sposito G (2008) The Chemistry of Soils. Oxford University Press.
- Bakatula EN, Richard D, Neculita CM, Zagury GJ (2018) Determination of point of zero charge of natural organic materials. Environ Sci Pollut Res. 25(8):7823-7833. doi:10.1007/s11356-017-1115-7
- Bhalkaran S, Wilson L (2016) Investigation of Self-Assembly Processes for Chitosan-Based Coagulant-Flocculant Systems: A Mini-Review. Int J Mol Sci. 2016;17(10):1662. doi:10.3390/ijms17101662
- Agatonovic-Kustrin S, Ramenskaya G, Kustrin E, Ortakand DB, Morton DW (2020) A new integrated HPTLC - ATR/FTIR approach in marine algae bioprofiling. J Pharm Biomed Anal. 189:113488. doi:10.1016/j.jpba.2020.113488
Schemes 1 to 3 are available in the Supplementary Files section
No competing interests reported.
- Scheme1.png
Scheme 1Crosslinking between silanol group of silica with the chitosan hydroxyl group to form chitosan/silica composite.
- Scheme2.png
Scheme 2 The schematic representation showing the crosslinking between the chitosan/silica composite and the glycerol hydroxyl group of chitosan silanol group.
- Scheme3.png
Scheme 3(a) Reaction between GPTEOS and silanol group of silica to form organosilicon compound. (b) The organosilicon compound can react with the chitosan through its hydroxyl group and amine.
- Supplementary.docx
