Desalination of dye utilizing carboxylated TiO2/calcium alginate hydrogel nanofiltration membrane with high salt permeation

Carrageenan/calcium alginate composite hydrogel filtration membranes for efficient cationic dye separation

The development of biopolymer-based filtration systems for water remediation applications is an extremely fascinating area of research. In this paper, we developed a biopolymer-based filtration system using sodium alginate (NaAlg) and carrageenan (Car) for the removal of the toxic cationic dye, methylene blue (MB). The membrane's properties were assessed using FTIR, TGA, UTM, FESEM, EDS, XRD, and water uptake, revealing commendable thermomechanical stability (5.79 MPa), good hydrophilicity, and compatibility. The experimental results further revealed that lambda Car/calcium alginate (λ-Car/CaAlg) exhibited superior dye rejection (100%) and flux (11.67 L m-2 h-1) compared to kappa Car/CaAlg (κ-Car/CaAlg) (99.22% and 11.19 L m-2 h-1) and plain alginate (CaAlg) (99.63% and 9.79 L m-2 h-1). The high MB rejection rate was attributed to the sieving mechanism and electrostatic interaction. A rejection rate of 100% was achieved at an initial MB concentration of 10 mg/L, pressure of 0.1 MPa, pH of 7, and temperature of 25°C. Furthermore, the hydrogel membranes demonstrated excellent recyclability over nine cycles, indicating their potential for water treatment applications.

Characterization of a chlorine resistant and hydrophilic TiO2/calcium alginate hydrogel filtration membrane used for protein purification maintaining protein structure

The development of membranes for protein purification has stringent requirement of disinfection resistance, low protein adsorption and anti-fouling, without changing protein structure. In this study, hydrophilic titanium dioxide (TiO2)/calcium alginate (TiO2/CaAlg) hydrogel membranes were prepared by a simple ionic cross-linking method. The effects of the porogenic agent polyethylene glycol (PEG) concentration, the molecular weight of PEG, and the concentration of TiO2 on the filtration properties were systematically investigated. The TiO2/CaAlg membrane exhibited excellent bovine serum albumin (BSA) rejection and anti-fouling properties. The mechanical properties and surface energy of the TiO2/CaAlg membrane were significantly improved. The chemical bonding mechanism of TiO2 and NaAlg was investigated by molecular dynamic simulation. The TiO2/CaAlg membrane had good chlorine resistance and could be disinfected or cleaned with sodium hypochlorite. The TiO2/CaAlg hydrogel membrane loaded with polyhydroxybutyrate (PHB) nanofibers maintained high flux (136.7 L/m2h) and high BSA rejection (98.0 %) at 0.1 MPa. The results of circular dichroism and synchronous fluorescence indicated that the secondary structure of BSA was maintained after membrane separation. This study provides one method for the preparation of green and environmentally friendly membrane for protein purification.

Sieving and Clogging in PEG-PEGDA Hydrogel Membranes

Hydrogels are promising systems for separation applications due to their structural characteristics (i.e., hydrophilicity and porosity). In our study, we investigate the permeation of suspensions of rigid latex particles of different sizes through free-standing hydrogel membranes prepared by photopolymerization of a mixture of poly(ethylene glycol) diacrylate (PEGDA) and large poly(ethylene glycol) (PEG) chains of 300,000 g·mol-1 in the presence of a photoinitiator. Atomic force microscopy and cryoscanning electron microscopy (cryoSEM) were employed to characterize the structures of the hydrogel membranes. We find that the 20 nm particle permeation depends on both the PEGDA/PEG composition and the pressure applied during filtration. In contrast, we do not measure a significant permeation of the 100 nm and 1 μm particles, despite the presence of large cavities of 1 μm evidenced by the cryoSEM images. We suggest that the PEG chains induce local nanoscale defects in the cross-linking of PEGDA-rich walls separating the micrometer-sized cavities, which control the permeation of particles and water. Moreover, we discuss the decline of the permeation flux observed in the presence of latex particles compared to that of pure water. We suggest that a thin layer of particles forms on the surface of the hydrogels.

Antifouling thin-film nanocomposite NF membrane with polyvinyl alcohol-sodium alginate-graphene oxide nanocomposite hydrogel coated layer for As(III) removal

Removal of As(III) from the polluted waters is a challenge. It should be oxidized to As(V) for increasing its rejection by RO membranes. However, in this research, As (III) is directly removed by a high permeable and antifouling membrane prepared through the surface coating and in-situ crosslinking procedure of polyvinyl alcohol (PVA) and sodium alginate (SA) as coating materials containing graphene oxide as a hydrophilic additive on a polysulfone support with glutaraldehyde (GA) chemical crosslinking agent. The properties of the prepared membranes were evaluated through contact angle, zeta potential, ATR-FTIR, SEM, and AFM. The addition of GO in the polymeric networks of SA and PVA hydrogel coating layers led to a better hydrophilicity and a smoother surface and a higher negative surface charge resulted in improvment of permeability and rejection of membranes. Among the prepared hydrogel-coated modified membranes, SA-GO/PSf indicated the highest pure water permeability (15.8 L m^-2 h^-1 bar^-1) and BSA permeability (9.57 L m^-2 h^-1 bar^-1), respectively. The best desalination performance (NaCl, MgSO₄, and Na₂SO₄ rejections of 60.0%, 74.5%, and 92.0%, respectively) and As(III) removal (88.4%) along with satisfactory stability and reusability in cyclic continuous filtration was reported for PVA-SA-GO membrane. In addition, the PVA-SA-GO membrane indicated improved fouling resistance toward BSA foulant with the lowest flux decline of 7%.

Biomimetic mineralization of nacre-inspired multiple crosslinked PVA/CaAlg/SiO2 membrane with simultaneously enhanced mechanical and separation properties

Inspired by the natural nacre structure, we propose a new strategy to fabricate mineralized, multiple crosslinked hydrogel membranes with the "rigid silica in soft polymer" nacre-like structure. In-situ SiO₂ nanoparticles (NPs) and polyvinyl alcohol/sodium alginate (PVA/NaAlg) are used to simulate the rigid "bricks" and soft "mortar" compositions of nacre, respectively. The nacre-like mineralized (PVA/CaAlg/SiO₂) membrane showed a higher tensile strength of 4.1 ± 0.08 MPa, excellent pure water flux of 170 ± 3 L/m²h, and an oil/water rejection rate of 99 %. The interwoven hierarchal structure, similar to nacre, was determined by SEM analysis. In addition, incorporating SiO₂ NPs increases the anti-swelling, roughness, and hydrophilicity of the membranes. PVA/CaAlg/SiO₂ membrane exhibited excellent superhydrophilicity (WCA value was 0°) and superoleophobicity underwater (OCA value was 162°). PVA/CaAlg/SiO₂ membrane also showed excellent separation performance for water-soluble organic pollutants and can be used for dye separation with rejection efficiencies of 99.5 %, 99.1 %, and 98.3 % for Congo red (CR), Alizarin red (AR), and Sunset yellow (SY), respectively. Moreover, PVA/CaAlg/SiO₂ membrane had outstanding long-term filtration and antifouling performance. The biomineralization-inspired structure provides a promising technique that can be used to prepare high-performance organic-inorganic membranes with great promise for wastewater separation application.

Cross-Linked and Doped Graphene Oxide Membranes with Excellent Antifouling Capacity for Rejection of Antibiotics and Salts

Graphene oxide (GO) membranes have suffered from the instability of water permeability and low rejection of pollutant separation. In this paper, a reasonable modification protocol for GO nanosheets at the molecular level was proposed. A molecular cross-linking strategy was adopted to regulate the interlayer spacing of GO nanosheets, and nanofiltration membranes with high water stability and excellent antifouling capacity were prepared, which could effectively reject antibiotics and salts. The GO₁-MPD_0.5 (the mass ratio of GO nanosheets to MPD is 1:0.5) and GO/GO₁-MPD_0.5-0.25 (the doping ratio of GO₁-MPD_0.5 is 25%) membranes had stable water permeability of 4.22 ± 0.06 and 3.65 ± 0.11 L m^-2 h^-1 bar^-1, and the rejection rates for ciprofloxacin (CIP) and ofloxacin (OFX) were 93.35 ± 3.62 and 95.48 ± 2.97 and 85.89 ± 6.52 and 88.21 ± 3.67%, respectively. Molecular dynamics simulations well explained the high water stability of membranes, and the cross-linked hydrophobic benzene ring played a role in the rejection of pollutant molecules. Moreover, the GO₁-MPD_0.5 membrane showed excellent antifouling capacity and the flux recovery ratio (FRR) was more than 98%. This paper provides a new idea for the design of nanofiltration membranes with high stability and good rejection permeability at the molecular level and provides a prospect for the application of nanofiltration membranes in practical water treatment and water purification.

Design of a new polyethersulfone nanofiltration membrane with anti-fouling properties using supported protic ionic liquid modification for dye/salt removal

Facile techniques to fabricate the nanofiltration membranes with ideal molecular sieving is one of the most interesting subjects in membrane separation technology. In this study, the application of modified graphene oxide (GO) with triethylenetetramine (TETA), CuFe₂ O₄ , and acetic acid (AC) (supported GO-TETA-CuFe₂ O₄ @AC) as a supported protic ionic liquid (PIL) modifier for polyethersulfone (PES) membrane was evaluated to approve the improvement of anti-fouling properties and wastewater rejection of the fabricated membranes. To enhance the key properties of graphene oxide, it was modified by hydrophilic nanomaterials (TETA-CuFe₂ O₄ ). High flux and promising flux recovery ratio (up to 95% compared to the unmodified membrane) can be observed in the modified membranes. The modified membranes by GO-TETA-CuFe₂ O₄ @AC were studied at optimum concentrations (0.5 wt.%) for salt rejection and different dyes. The obtained data indicated that the modified membranes by GO-TETA-CuFe₂ O₄ @AC indicated higher salt removal (up to 97% for BaCl₂ than the unmodified membrane), which was related to the efficient modification. The obtained pure water flux (PWF) for bare and optimal modified membrane from 13.11 to 27.87 kg/m² ·h, respectively. To exact evaluate the effect of membrane modification on performance examination, the modified membranes were evaluated for chlorine resistance testing. This study aimed to develop cost-effective nanofiltration (NF) membranes with high anti-fouling properties and to determine the maximum filtration capacity of in-time dyes and salts in effluents. PRACTITIONER POINTS: A GO-TETA-CuFe2O4 mixed matrix membrane was prepared for removal of salts and dyes. The effect of GO-TETA-CuFe2O4 enhanced the hydrophilicity and porosity. The membrane exhibited superior antifouling properties and ions rejection.

Development of Functional Hybrid Polymers and Gel Materials for Sustainable Membrane-Based Water Treatment Technology: How to Combine Greener and Cleaner Approaches

Water quality and disposability are among the main challenges that governments and societies will outside during the next years due to their close relationship to population growth and urbanization and their direct influence on the environment and socio-economic development. Potable water suitable for human consumption is a key resource that, unfortunately, is strongly limited by anthropogenic pollution and climate change. In this regard, new groups of compounds, referred to as emerging contaminants, represent a risk to human health and living species; they have already been identified in water bodies as a result of increased industrialization. Pesticides, cosmetics, personal care products, pharmaceuticals, organic dyes, and other man-made chemicals indispensable for modern society are among the emerging pollutants of difficult remediation by traditional methods of wastewater treatment. However, the majority of the currently used waste management and remediation techniques require significant amounts of energy and chemicals, which can themselves be sources of secondary pollution. Therefore, this review reported newly advanced, efficient, and sustainable techniques and approaches for water purification. In particular, new advancements in sustainable membrane-based filtration technologies are discussed, together with their modification through a rational safe-by-design to modulate their hydrophilicity, porosity, surface characteristics, and adsorption performances. Thus, their preparation by the use of biopolymer-based gels is described, as well as their blending with functional cross-linkers or nanofillers or by advanced and innovative approaches, such as electrospinning.

Polyvinyl alcohol and sodium alginate hydrogel coating with different crosslinking procedures on a PSf support for fabricating high-flux NF membranes

Polyvinyl alcohol (PVA) and sodium alginate (SA) hydrogel-coated nanofiltration (NF) membranes with high-flux and permselectivity were prepared. The coating of PVA and SA hydrogel selective layer on a porous polysulfone (PSf)/non-woven fabric ultrafiltration substrate membrane was conducted through different three procedures including pre-crosslinking, in-situ crosslinking, and immersing crosslinking and the use of glutaraldehyde as a crosslinking agent. The properties and performances of all types of the prepared membranes were evaluated through ATR-FTIR spectroscopy, AFM, SEM, zeta potential, contact angle, and cross-flow permeation tests. The immersing technique resulted in the formation of TFC membranes with higher hydrophilicity, smoother surface layer, higher negative charge, higher permeation flux, higher salt rejection and better anti-fouling performance. Also, the higher negative surface charge of the immersing coated TFC membranes due to dissociation of hydrophilic functional groups of the PVA and SA hydrogel selective layer resulted in higher As(III) rejection. SA coated NF membrane through immersing method exhibited a higher pure water permeability of 11.2 L m^-2 h^-1 bar^-1, NaCl, MgSO₄, and Na₂SO₄ rejection of 38.2%, 55.1%, and 70.4%, respectively with As(III) rejection of 60.6%. All types of the PVA and SA hydrogel-coated PSf membranes possessed improved fouling resistance to BSA aqueous solution, superior anti-fouling performance was obtained with SA hydrogel coating through immersing method. Such optimum membranes indicated high stability in the long-term experiments. This study showed that the coating of the SA hydrogel layer on a PSf support through immersing method could be a promising candidate for fabricating high-flux NF membranes.

Recent trends and challenges with the synthesis of membranes: Industrial opportunities towards environmental remediation

The industrial and agricultural revolution has posed a serious and potential threat to environment. The industrial and agricultural pollutants are directly released into the environment. This issue has clinched the scientists to work on different materials in order to decontaminate the environment. Among all other techniques, the membrane filtration technology has fascinated researchers to overcome the pollution by its promising features. This review elaborated various membrane synthesis approaches along with their mechanism of filtration, their applications towards environmental remediation such as removal of heavy metals, degradation of dyes, pharma waste, organic pollutants, as well as gas sensing applications. The membrane synthesis using different sort of materials in which inorganic, carbon materials, polymers and metal organic framework (MOFs) are highlighted. These materials have been involved in synthesis of membrane to make it more cost effective and productive to remove such hazardous materials from wastewater. Based on the reported literature, it has been found that inorganic and polymer membranes are facing issues of brittleness and swelling prior to the industrial scale applications related to the high temperature and pressure which needs to be addressed to enhance the permeation performance.

MXene-regulation polyamide membrane featuring with bubble-like nodule for efficient dye/salt separation and antifouling performance

Removing salt from dye/salt mixtures using nanofiltration (NF) membranes needs to be improved to ensure high permeability, high selectivity, and antifouling performance. In this study, we used an interfacial polymerization (IP) technique to create a novel thin-film nanocomposite NF membrane by introducing two-dimensional MXene Ti₃C₂T_x into the polyamide (PA) layer. Enhanced IP reaction rate facilitated the overflow of residual solvent from the fresh PA layer's edge due to the MXene-mediated IP strategy, resulting considerable bubble-like nodules on the membrane surface. The unique nanostructure of PA effective layer could be tuned by controlling the MXene concentration in aqueous phase solution, which finally promoted the obtained membranes with superb permselectivity. In this way, the water permeability was elevated to a maximum value of 45.12 L m⁻¹ h⁻¹, nearly 1.58-fold compared to the PA-pristine membrane. Moreover, the Ti₃C₂T_x/NF membrane exhibited a superior dye/monovalent salt separation coefficient of 820, outperforming the pristine PA membrane and other NF membranes in the literature. Additionally, the MXene-assisted IP strategy designed an effective dye anti-fouling hydration layer, which played a crucial role in fouling resistance. This work illustrates a novel use of Ti₃C₂T_x to successfully regulate high-performance TFN PA membranes for potential application in dye/salt separation.

A novel thin-film nanocomposite NF membrane with efficient dye/salt separation and antifouling performance was designed by introducing different amounts of MXene into the PA layer.

Recovery of Model Pharmaceutical Compounds from Water and Organic Solutions with Alginate-Based Composite Membranes

In this work, we combined the non-solvent induced phase separation (NIPS) and further cross-linking by cations towards the preparation of nanofiltration membranes based on sodium alginate, a biodegradable, natural polymer. Acetone, ethanol, toluene, and hexane were used as non-solvents, and cations of calcium, silver, and aluminum—for polymer cross-linking, respectively. Results showed the precipitation strength of non-solvent played a noticeable role in the membrane’s performance; for instance, the toluene permeability changed by four orders of magnitude with the decrease of precipitation strength of the non-solvent: acetone (P_toluene = 0.1 kg∙m⁻²∙h⁻¹∙bar⁻¹) < ethanol (3 kg∙m⁻²∙h⁻¹∙bar⁻¹) < hexane (41 kg∙m⁻²∙h⁻¹∙bar⁻¹) < toluene (415 kg∙m⁻²∙h⁻¹∙bar⁻¹). It was shown that simultaneous precipitation and crosslinking in aqueous solutions AlCl₃ or AgNO₃ must be used in the preparation of alginate membranes for the highly selective recovery of pharmaceutical compounds from organic media. These membranes show rejection R = 90–93% of substances with MW = 626 g/mol and ethanol permeability P_EtOH = 1.5–2.5 kg∙m⁻²∙h⁻¹∙bar⁻¹. For the highly selective recovery of pharmaceutical compounds from water, the method of obtaining membranes must be changed. Precipitation in toluene and then crosslinking in aqueous solutions of AlCl₃ or AgNO₃ must be used sequentially instead of simultaneous precipitation and crosslinking in aqueous solutions of the same inorganic salts. The permeability of such membranes varied from 0.44 to 7.8 kg∙m⁻²∙h⁻¹∙bar⁻¹ depending on the crosslinking cation in the alginate. The rejection of model substances with MW 350 and 626 g/mol were on the level of 99%. Alginate membranes can be used to solve separation problems in the pharmaceutical field, for example, to isolate antibiotics from their extractants and remove the same antibiotics from aqueous pharmaceutical waste to prevent their accumulation in the environment and the emergence of resistant genes and bacteria.

High-performance TFNC membrane with adsorption assisted for removal of Pb(II) and other contaminants

Rapid and thorough removal of heavy metal ions in wastewater is critical for the urgent need of clean water. Herein, we prepared a high-performance thin film nanofibrous composite (TFNC) membrane consisting of a polyacrylonitrile (PAN)-UiO-66-(COOH)₂ composite nanofibrous substrate (CPAN) and a calcium alginate (CaAlg) skin layer. Owing to abundant adsorption sites of UiO-66-(COOH)₂ MOF, the optimal CPAN-2 nanofibrous substrate showed excellent adsorption capacity for lead ions. The maximum Pb²⁺ adsorption capacity of CPAN-2 substrate calculated by Langmuir isotherm model was 254.5 mg/g. Meanwhile, due to the relatively loose structure of CaAlg skin layer, this TFNC membrane showed high water permeate flux about 50 L m^-2h^-1 at 0.1 MPa, and the rejection for dyes was higher than 95%. Therefore, CaAlg/CPAN TFNC membranes were appropriate for dynamic adsorption/filtration to remove Pb²⁺. Compared with original CaAlg/PAN membrane, the optimal CaAlg/CPAN TFNC membrane showed much better ability to treat Pb(II)-containing wastewater and had good recyclability. Most importantly, the CaAlg/CPAN TFNC membrane could treat 7659 L m^-2 wastewater containing single lead ions under WHO drinking water standard, and effectively deal with more simulated lead-containing wastewater. This work could provide a substitutable solution for effective removal of heavy metal ions and other various contaminants in wastewater.

High Flux and Antifouling Nanofiltration Membrane Modified by Ag@UiO-66-NH2 and Its Application for Biphenol A Removal

Owing to the specific porous structure which could provide additional passage channel for some molecules, metal organic frameworks are attractive candidates for enhancing permeability and selectivity of membranes in pervaporation, reverse osmosis, and gas separation. In this experiment, Ag@UiO-66-NH2 was introduced into polyamide separation layer by interfacial polymerization of triethylenetetramine and 1,3,5-benzenetricarboxylic acid chloride for nanofiltration. The results indicated that Ag@UiO-66-NH2 nanoparticles did endow the membranes with rapid diffusion pathways for water molecules. When the content of Ag@UiO-66-NH2 was 0.03 g, the prepared membrane (NF-Ag-3) showed high flux about 47.3 L·m-2·h-1 at 0.6 MPa, which is about 2-fold higher than that of polyamide membrane without Ag@UiO-66-NH2, while the MgSO4 rejection rate remained about 87.4%. The membrane also showed excellent antifouling properties, and the water flux recovery ratio was 95.6% after filtration BSA solution. When it was applied for 50 mg/L bisphenol A removal, the rejection rate reached 94.6%, and the flux is about 49.1 L·m-2·h-1. Moreover, Ag particles on UiO-66-NH2 rendered the membrane with good inhibition for Escherichia coli. The antibacterial rate of the membranes is above 95% when the loading of Ag@UiO-66-NH2 is more than 0.03 g.

Facile Preparation and Dye Adsorption Performance of Poly(N-isopropylacrylamide-co-acrylic acid)/Molybdenum Disulfide Composite Hydrogels

Using N-isopropylacrylamide (NIPAM) and acrylic acid (AAc) as monomers, N,N'-methylenebisacrylamide (MBA) as a cross-linking agent, and molybdenum disulfide (MoS2) as functional particles, a P(NIPAM-co-AAc)/MoS2 composite hydrogel was prepared by free radical polymerization initiated by ultraviolet light. The results of Fourier transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy show that MoS2 has been successfully introduced into the P(NIPAM-co-AAc) system, and the obtained composite hydrogel has a porous network structure. Studies on the swelling property and dye adsorption performance show that the addition of MoS2 can increase the swelling ratio of P(NIPAM-co-AAc) hydrogels to a certain extent and can significantly improve the ability of the P(NIPAM-co-AAc) hydrogel to adsorb methylene blue (MB). The adsorption process of MB by the composite hydrogels conforms to the pseudo-second-order kinetics and the Langmuir isotherm adsorption models. The estimated equilibrium adsorption capacity (Q m) using the Langmuir isotherm model can reach 1258 mg/g, mainly due to the electrostatic interaction between the negatively charged groups -COO- and MoS2 particles on the network structure and the positively charged dye MB. The adsorption of MB by P(NIPAM-co-AAc)/MoS2 composite hydrogels depends on the temperature during adsorption. Compared with room temperature, a high temperature of 40 °C above the poly(N-isopropylacrylamide) (PNIPAM) phase transition temperature (∼32 °C) leads to a decreased adsorption capacity of the P(NIPAM-co-AAc)/MoS2 composite hydrogel for MB due to the enhanced hydrophobic properties of the network structure and the decrease of the swelling ratio. The prepared hydrogel material can be used as a good adsorbent for dyes, which is promising in wastewater treatment.

Adsorption properties of β-cyclodextrin modified hydrogel for methylene blue

With the development of dye and printing, production wastewater has become one of the most primary pollution sources of water and soil pollution. Most of the dyes are toxic substances, which have the "three-way" effect of carcinogenic, teratogenic and mutagenic. Therefore, it is a very difficult but significant issue to deal with the dye in the wastewater. Here, we report a study on low-cost, high-capacity hydrogels that remove water-soluble dyes. The hydrogel is prepared by crosslinking the β-cyclodextrin and functional monomer: acrylamido and 2-acrylamide-2-methylpropane sulfonic acid by aqueous solution polymerization, meanwhile, alkaline hydrolysis is also an important step for adsorption performance. After alkaline hydrolysis, the amide and sulfonic groups in the hydrogel were converted into carboxylate and sulfonate, which was beneficial to the adsorption of cationic dyes. This polymer could remove 96.58% methylene blue (400 mg/L) and only requires 0.02 wt%. Its maximum adsorption capacity for methylene blue could reach 2638.22 mg/g under equilibrium condition. It is the most powerful adsorbent used to treat dye wastewater, according to the report. It also provides some references for hydrogel treatment of dye wastewater.

Properties and potential applications of mannuronan C5-epimerase: A biotechnological tool for modifying alginate

Given the excellent characteristics of alginate, it is an industrially important polysaccharide. Mannuronan C5-epimerase (MC5E) is an alginate-modifying enzyme that catalyzes the conversion of β-D-mannuronate (M) to its C5 epimer α-L-guluronate (G) in alginate. Both the biological activities and physical properties of alginate are determined by M/G ratios and distribution patterns. Therefore, MC5E is regarded as a biotechnological tool for modifying and processing alginate. Various MC5Es derived from brown algae, Pseudomonas and Azotobacter have been isolated and characterized. With the rapid development of structural biology, the crystal structures and catalytic mechanisms of several MC5Es have been elucidated. It is necessary to comprehensively understand the research status of this alginate-modifying enzyme. In this review, the properties and potential applications of MC5Es isolated from different kinds of organisms are summarized and reviewed. Moreover, future research directions of MC5Es as well as strategies to enhance their properties are elucidated, highlighted, and prospected.

Low-viscosity sodium alginate combined with TiO2 nanoparticles for improving neuroblastoma treatment

Titanium dioxide (TiO₂) nanoparticles have been explored to prevent various cancer developments but it may cause oxidation, inflammation and high cytotoxicity. Alginate has nontoxic, anti-inflammatory, and antioxidant effects. We aimed to explore the effects of alginate-TiO₂ temozolomide (TMZ) nanoparticles on neuroblastoma. A neuroblastoma model was established with neuroblastoma cells and alginate-TiO₂ TMZ nanoparticles were made by spraying low-viscosity sodium alginate (250-360 kDa). The morphology of nanoparticles was observed via scanning electron microscope (SEM). The crystallinity values were analyzed via X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic study. Neuroblastoma mice were treated with saline solution, TMZ, TiO₂-TMZ and alginate-TiO₂-TMZ nanoparticles. Anti-oxidant, anti-inflammatory, and anti-tumor properties and the mouse survival rates were measured. The spectrometric profiles of alginate-TiO₂ were consistent with those of TiO₂ and alginate. Alginate-TiO₂ TMZ nanoparticles had higher cytotoxicity toward neuroblastoma cells and less inhibitory activity toward normal neuronal cells. The combined nanoparticles increased antioxidant, anti-inflammatory and antitumor activities and prolonged the survival time of the neuroblastoma model (P < 0.05). On the other hand, Alginate-TiO₂ TMZ nanoparticles reduced the levels of mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB). The combined nanoparticles improved neuroblastoma treatment by affecting NF-κB and MAPK signals.