Recent advances in exploitation of nanomaterial for arsenic removal from water: a review

Nanoconfinement boosts affinity of hydrated zirconium oxides to arsenate: Surface complexation modeling study

Nanoscale hydrated zirconium oxide (HZO) holds great potential in groundwater purification due to its ability to form inner-sphere coordination with arsenate. Despite being frequently used, especially as encapsulations in host materials for practical application in water treatment, the adsorption mechanisms of solutes on HZO are not appropriately explored, in particular for arsenate adsorption. In this study, we investigated the Zr-As coordination configuration and identified the most credible Zr-As configuration using surface complexation modeling (SCM), XPS and FT-IR analysis. The corresponding intrinsic coordination constants (Kintr) values was calculated by SCM, and the nanoconfinement effects were distinguished by comparing bare HZO with the HZO nanoparticles (NPs) encapsulated inside the strongly basic anion exchanger D201. Potentiometric titration suggests that the surface Zirconium hydroxyl groups (≡ZrOH) mainly exist in protonated form (≡ZrOH2+). Batch adsorption experiments demonstrate that the D201 hosts could adsorb As(V) through ion exchange by the quaternary ammonium groups under the low ionic strength (≤0.01 M NaNO3) and at pH > 6. The nanocomposite (HZO@D201) exhibits a higher adsorption capacity in a wide range of pH (3-10) and ionic strength (0.001-0.1 M NaNO3) than bare HZO. SCM simulations reveal that the coordination configuration of diprotonated monodentate mononuclear (MM-H2) dominates at pH 3-6, while deprotonated bidentate binuclear (BB-H0) dominates at pH > 7. For each configuration, the intrinsic coordination constants (Kintr) of HZO@D201 (10-0.66 and 10-16.10, respectively) are significantly higher than those of bare HZO (10-12.24 and 10-44.42, respectively), indicating a superior chemical bonding affinity caused by nanoconfinement. The obtained Kintr values are used to predict arsenate adsorption isotherms in pH 3 and 9, and the results align with the SCM simulation outcomes. This study may offer a feasible method for investigating the nanoconfinement effect of emerging nanocomposite adsorbents from a thermodynamic perspective, and provide reference coordination equilibrium constants of HZO for research and practical application.

Self-Competitive Adsorption Behavior of Arsenic on the TiO2 Surface

TiO2 is a commonly used material to remove arsenic from drinking water by adsorption as well as photocatalytic oxidation (PCO). In the present paper, arsenic adsorption and PCO at different pH environments are studied on the (1 1 0) facet of rutile TiO2 (r-TiO2). A self-competitive adsorption (SCA) behavior of arsenic is observed; i.e., arsenic species compete to adsorb on the surface. Related DFT calculations are carried out to simulate adsorption. SCA behavior is the key to connecting calculation results with experimental results. Furthermore, PCO of arsenite is performed at different pH values. Of note, PCO is related to adsorption; namely, the adsorption process determines the whole PCO reaction speed. Therefore, SCA is also helpful for the PCO reaction. The SCA behavior is useful not only for arsenic on r-TiO2 but also for arsenic on anatase TiO2 (a-TiO2). It may be helpful to further study arsenic adsorption and PCO on other materials such as Fe2O3 and MnO2. The SCA behavior extends our understanding of arsenic and provides new insights into arsenic removal and its cycle in nature.

Magnetic solid phase extraction as a nonchromatographic method for the quantification of ultratrace inorganic arsenic in rice by inductively coupled plasma-optical emission spectrometry (ICP OES)

An alternative analytical method was developed for the quantification of inorganic arsenic (iAs) in rice by ICP OES. Iron nanoparticles modified with an organophosphorus compound were used as the solid phase for MSPE of iAs from the plant matrix. The MSPE procedure was performed using 4 mL of a buffer solution with pH 4.0, 20 mg of the nanomaterial, and a 15-min extraction time. The total As (tAs) by ICP OES was also quantified using the same MSPE procedure after solubilization of the samples by a block digester. The accuracy of tAs and iAs quantification was verified using CRM NIST 1568b (97 % and 101 % recovery, respectively). The precision (RSD < 15 %) and LOD and LOQ (1.08 and 3.70 µg kg^-1, respectively) of the proposed method were satisfactory. The rice samples had tAs contents between 0.090 and 0.295 mg kg^-1 and iAs mass fractions between 0.055 and 0.109 mg kg^-1.

Simultaneous precipitation and discharge plasma processing for one-step synthesis of α-Fe2O3-Fe3O4/graphene visible light magnetically separable photocatalysts

A novel facile combination of precipitation and plasma discharge reaction is successfully employed for one-step synthesis of an α-Fe₂O₃-Fe₃O₄ graphene nanocomposite (GFs). The co-existence and anchoring of hematite (α-Fe₂O₃) and magnetite (Fe₃O₄) nanoparticles onto a graphene sheet in the as synthesized GFs were verified by results of XRD, Raman, SEM, TEM, and XPS. HRTEM characterization was used for confirming the bonding between α-Fe₂O₃/Fe₃O₄ nanoparticles and the graphene sheet. Consequently, GFs shows superior photodegrading performance towards methylene blue (MB), compared to individual α-Fe₂O₃/Fe₃O₄ nanoparticles, as a result of band gap narrowing and the electron-hole pair recombination rate reducing. Moreover, GFs allows a good possibility of separating and recycling under an external-magnetic field, suggesting potential in visible-light-promoted photocatalytic applications.

Effective biosorption of As(V) from polluted water using Fe(III)-modified Pomelo (Citrus maxima) peel: A batch, column, and thermodynamic study

Pomelo, Citrus maxima, peel was chemically modified with lime water and then loaded with Fe(III) to develop anion exchange sites for effective sequestration of As(V) from water. Biosorbent characterizations were done by using FTIR, SEM, XRD, EDX, and Boehm's titration. The batch biosorption studies were carried out at various pHs using modified and non-modified biosorbents and optimum biosorption of As(V) occurred at acidic pH (3.0-5.0) for both the biosorbents. A kinetic study showed a fast biosorption rate and obtained results fitted well with the pseudo-second-order (PSO) model. When isotherm data were modeled using the Langmuir and Freundlich isotherm models, the Langmuir isotherm model fit the data better and produced maximal As(V) biosorption capacities of 0.72 ± 03, 0.86 ± 06, and 0.95 ± 05 mmol/g at temperatures 293± 1K, 298± 1K and 303± 1K, respectively. Desorptionof As(V) was effective using 0.1 M NaOH in batch mode. Negative values of ΔG° for all temperatures with positive ΔH° confirmed the spontaneous and endothermic nature of As(V) biosorption. The existence of co-existing chloride (Cl^-), nitrate (NO₃ ^-), sodium (Na⁺), and calcium (Ca²⁺) showed insignificant interference whereas a high concentration of sulphate (SO₄ ^2-) and phosphate (PO₄ ^3-) significantly lowered As(V) biosorption percentage. Arsenic concentrations in actual arsenic polluted groundwater could be reduced to the WHO drinking water standard (10 μg/L) by using only 1 g/L of investigated Fe(III)-SPP. The dynamic biosorption of As(V) in a fixed bed system showed that Fe(III)-SPP was effective also in continuous mode and different design parameters for fixed bed system were determined using Thomas, Adams-Bohart, BDST, and Yoon-Nelson models. Therefore, from all of these results it is suggested that Fe(III)-SPP investigated in this study can be a potential, low cost and environmentally benign biosorbent material for an effective removal of trace amounts of arsenic from polluted water.

Recovery of Metals from Wastewater-State-of-the-Art Solutions with the Support of Membrane Technology

This paper discusses the most important research trends in the recovery of metals from industrial wastewater using membrane techniques in recent years. Particular attention is paid to the preparation of new membranes with the required filtration and separation properties. At the same time, possible future applications are highlighted. The aspects discussed are divided into metals in order to clearly and comprehensibly list the most optimal solutions depending on the composition of the wastewater and the possibility of recovering valuable components (metalloids, heavy metals, and platinum group metals). It is shown that it is possible to effectively remove metals from industrial wastewater by appropriate membrane preparation (up to ~100%), including the incorporation of functional groups, nanoparticles on the membrane surface. However, it is also worth noting the development of hybrid techniques, in which membrane techniques are one of the elements of an effective purification procedure.

Nonthermal plasma-irradiated polyvalent ferromanganese binary hydro(oxide) for the removal of uranyl ions from wastewater

Nonthermal plasma (NTP) irradiation was employed to adjust the morphological structures and valence distribution of ferromanganese (Fe-Mn)-based binary hydro (oxide) to enhance the heterogeneous adsorption of uranyl ions. The output voltage and the liquid-plate distance played a more vital role among the NTP factors in the irradiation system in influencing the polyvalent Fe-Mn binary hydro (oxide) (poly-Fe-Mn). The formation of plates, flakes, and nanoscale nodules was specifically observed, which caused more pores and fractures in the poly-Fe-Mn binary hydro (oxide). The poly-Fe-Mn performed explicitly better in the adsorption of uranium ions in comparison with the counterpart of the Fe-Mn, which was appropriately fitted by the pseudofirst-order kinetic and Elovich models. Maximum equilibrium adsorption capacities of 663.92 and 923.45 mg/g were obtained for the Fe-Mn and poly-Fe-Mn binary hydro (oxides) toward U ions in the orthogonal design, respectively. The maximum monolayer adsorption capacity achieved by the fitting of the Langmuir model was 1091.10 mg/g. Both physisorption and chemisorption contributed to the heterogeneous process of the poly-Fe-Mn toward uranium ions. The employment of NTP irradiation changed the monolayer adsorption of the traditional Fe-Mn materials and diversified the reaction mechanisms between the interface of the Fe-Mn materials and uranium ions. The elements, including O, N, and U exhibited higher compatibility and overlapped in the samples. The highly effective capture of uranium ions from the solution by the poly-Fe-Mn binary hydro (oxide) was mainly related to the chemical deposition of O and N radicals.

Removal of Organic Pollutants with Polylactic Acid-Based Nanofiber Composites

In the process of using nano-titanium dioxide (TiO2) photocatalytic treatment of organic polluted liquid, the easy aggregation and recycling difficulty of nano-TiO2 particles are important problems that cannot be avoided. Anchoring nano-TiO2 to the substrate not only limits the aggregation of nano-TiO2, but also facilitates the easy removal and reuse of nano-TiO2 after processing. Herein, coaxial electrospun nanofibrous (NFs) made of L-polylactic acid (PLLA) and chitosan (CS) are coated with graphene oxide (GO) and TiO2 for the enhanced oxidation of organic pollutants. The adsorption and photocatalysis experiment results show that, for methyl orange (MO) dye solution, the saturated removal of MO by PLLA/CS, PLLA/CS-GO and PLLA/CS-GO/TiO2 nanofibers are 60.09 mg/g, 78.25 mg/g and 153.22 mg/g, respectively; for the Congo red (CR) dye solution, the saturated removal of CR by PLLA/CS, PLLA/CS-GO and PLLA/CS-GO/TiO2 nanofiber materials were 138.01 mg/g, 150.22 mg/g and 795.44 mg/g, respectively. These three composite nanofiber membrane materials can maintain more than 80% of their adsorption capacity after four repeated cycles. They are environmentally friendly and efficient organic pollution remediation materials with promising application.

Parasitic Light Absorption, Rate Laws and Heterojunctions in the Photocatalytic Oxidation of Arsenic(III) Using Composite TiO2 /Fe2 O3

Composite photocatalyst‐adsorbents such as TiO₂/Fe₂O₃ are promising materials for the one‐step treatment of arsenite contaminated water. However, no previous study has investigated how coupling TiO₂ with Fe₂O₃ influences the photocatalytic oxidation of arsenic(III). Herein, we develop new hybrid experiment/modelling approaches to study light absorption, charge carrier behaviour and changes in the rate law of the TiO₂/Fe₂O₃ system, using UV‐Vis spectroscopy, transient absorption spectroscopy (TAS), and kinetic analysis. Whilst coupling TiO₂ with Fe₂O₃ improves total arsenic removal by adsorption, oxidation rates significantly decrease (up to a factor of 60), primarily due to the parasitic absorption of light by Fe₂O₃ (88 % of photons at 368 nm) and secondly due to changes in the rate law from disguised zero‐order kinetics to first‐order kinetics. Charge transfer across this TiO₂‐Fe₂O₃ heterojunction is not observed. Our study demonstrates the first application of a multi‐adsorbate surface complexation model (SCM) towards describing As(III) oxidation kinetics which, unlike Langmuir‐Hinshelwood kinetics, includes the competitive adsorption of As(V). We further highlight the importance of parasitic light absorption and catalyst fouling when designing heterogeneous photocatalysts for As(III) remediation.

Recent advances of magnetite nanomaterials to remove arsenic from water

Pure water is one of the major requirements for living beings but water bodies are contaminated with toxic pollutants and heavy metals. Around 225–500 million people on the earth depend on groundwater, which is highly contaminated by arsenic. Arsenic impurities are present in water as arsenite As(iii) and arsenate As(v). Arsenic is a highly toxic metalloid ranking one in toxicity. Researchers have been exploring new techniques and methods to purify water. Magnetic nanoparticles have high absorption and reaction capabilities due to their high surface-to-volume ratio and quantum size effects. Due to their high magnetization, adsorption behaviour, and biodegradability, magnetite nanomaterials are considered excellent materials to purify water. These nanomaterials and their composites are cost-effective as well as they can be easily separated, regenerated, and reused. This review gives a recent overview of the potential of magnetite nanoparticles and their composites to treat contaminated water and remove unwanted arsenic impurities.

Pure water is one of the major requirements for living beings but water bodies are contaminated with toxic pollutants and heavy metals.

Meso- and macroporous silica-based arsenic adsorbents: effect of pore size, nature of the active phase, and silicon release

Arsenic pollution in ground and drinking water is a major problem worldwide due to the natural abundance of arsenic by dissolution from ground sediment or mining activities from anthropogenic activities. To overcome this issue, iron oxides as low-cost and non-toxic materials, have been widely studied as efficient adsorbents for arsenic removal, including when dispersed within porous silica supports. In this study, two head-to-head comparisons were developed to highlight the As(v)-adsorptive ability of meso- and macrostructured silica-based adsorbents. First, the role of the textural properties of a meso-(SBA15) and macrostructured (MOSF) silica support in affecting the structural-morphological features and the adsorption capacity of the active phase (Fe2O3) have been studied. Secondly, a comparison of the arsenic removal ability of inorganic (Fe2O3) and organic (amino groups) active phases was carried out on SBA15. Finally, since silica supports are commonly proposed for both environmental and biomedical applications as active phase carriers, we have investigated secondary silicon and iron pollution. The batch tests at different pH revealed better performance from both Fe2O3-composites at pH 3. The values of q m of 7.9 mg g-1 (53 mg gact -1) and 5.5 mg g-1 (37 mg gact -1) were obtained for SBA15 and MOSF, respectively (gact stands for mass of the active phase). The results suggest that mesostructured materials are more suitable for dispersing active phases as adsorbents for water treatment, due to the obtainment of very small Fe2O3 NPs (about 5 nm). Besides studying the influence of the pore size of SBA15 and MOSF on the adsorption process, the impact of the functionalization was analyzed on SBA15 as the most promising sample for As(v)-removal. The amino-functionalized SBA15 adsorbent (3-aminopropyltriethoxysilane, APTES) exhibited a q m of 12.4 mg g-1 and faster kinetics. Furthermore, issues associated with the release of iron and silicon during the sorption process, causing secondary pollution, were evaluated and critically discussed.

Superior removal of As(III) and As(V) from water with Mn-doped β-FeOOH nanospindles on carbon foam

Arsenic pollution of water is one of the severest environmental challenges threatening human health. Iron-based nanomaterials have been demonstrated effective in arsenic removal. However, they generally suffer from low removal efficiency towards highly toxic As(III), loss of active sites owing to agglomeration, and poor reusability. Herein, we report a carbonized melamine foam supported Mn(IV)-doped β-FeOOH nanospindles(CF@Mn-FeOOH NSp) for tackling the technical hurdles. The designed CF@Mn-FeOOH NSp appears as a free-standing monolith through a low-cost and straightforward hydrothermal method. The atomic-scale integration of Mn(IV) into β-FeOOH enables an oxidation-adsorption bifunctionality, where Mn(IV) serves as oxidizer for As(III) and Fe(III) acts as adsorber for As(V). The maximal adsorption capacity for As(V) and As(III) can reach 152 and 107 mg g^-1, respectively. Meanwhile, As in simulated high arsenic groundwater can be decreased to below 10 μg L^-1 within 24 h. By simple "filtrating-washing", 85% and 82% of its initial adsorption capacity for As(V) and As(III) can be easily recovered even after 5-cycles reuse. Kinetics and isotherm adsorption study indicate that the arsenic adsorption behavior is mainly through chemical bonding during single-layer adsorbing process. The as-prepared CF@Mn-FeOOH offers a scalable, efficient, and recyclable solution for arsenic removal in groundwater and wastewater from mines and industry.

Oxygen-rich poly-bisvanillonitrile embedded amorphous zirconium oxide nanoparticles as reusable and porous adsorbent for removal of arsenic species from water

A new oxygen-rich porous polymer based on bisvanillonitrile was synthesized and characterized. This polymer was employed as support for the anchoring of 14.5 w% amorphous zirconium oxide nanoparticles. The formation of homogeneously dispersed nanoparticles in the poly-bisvanillonitrile (PBVN) host material was confirmed using N₂-sorption, XRPD, XPS and electron microscopy. The combination of zirconium oxide nanoparticles having active adsorption sites with the porous supporting material showed excellent adsorption of arsenic species. The resulting adsorption capacities of the hybrid material extend to 245 mg g^-1 for arsenite (As^III) and 115 mg g^-1 for arsenate (As^V). Moreover, adsorption kinetics showed a fast removal of both arsenic species with initial adsorption rate h of 0.0646 mg g^-1 min^-1 for arsenite and 0.0746 mg g^-1 min^-1 for arsenate. The immobilization was not interfered by the presence of other compounds in solution, indicating the applicability in real working environments. The material could be regenerated in a continuous mode using a 0.1 mol L^-1 sodium hydroxide solution at 70 °C to desorb arsenic.

Synthesis, characterization and application of magnetic nanoparticles modified with Fe-Mn binary oxide for enhanced removal of As(III) and As(V)

Arsenic contamination of drinking water sources is a widespread global problem. Of the As species commonly found in groundwater, As(III) is generally more mobile and toxic than As(V). In this work, magnetic nanoparticles (MNp) modified with Fe-Mn binary oxide (MNp-FeMn) were synthesized in order to develop a low cost adsorbent with high removal efficiency for both arsenic species which can be readily separated from water using a magnetic field. MNp-FeMn were characterized using different techniques including SEM/EDS, XRD and BET analysis. Adsorption of As(III) and As(V) on MNp-FeMn was studied as a function of initial arsenic concentration, contact time, pH, and coexisting anions. The BET specific surface area of MNp-FeMn was 109 m²/g and maghemite (γ-Fe₂O₃) was the dominant precipitated phase. The adsorption rate of As(III) and As(V) on MNp-FeMn was controlled by surface diffusion. FTIR analysis confirms that surface complexation through ligand exchange was the main mechanism for As(III) and As(V) removal on MNp-FeMn, with As(III) conversion to As(V) occurring on the adsorbent surface. The maximal adsorption capacity q_max of MNp for As(III) (26 mg/g) was significantly improved after modification with Fe-Mn binary oxide (56 mg/g), while q_max for As(V) was 51 and 54 mg/g, respectively. PO43-, SiO32- and CO32- reduced As(III) and As(V) uptake at higher concentrations. MNp-FeMn can be easily regenerated and reused with only a slight reduction in adsorption capacity. The high oxidation and sorption capacity of MNp-FeMn, magnetic properties and reusability, suggest this material is a highly promising adsorbent for treatment of arsenic contaminated groundwater.

Magnetic Nanoparticle Composites: Synergistic Effects and Applications

Composite materials are made from two or more constituent materials with distinct physical or chemical properties that, when combined, produce a material with characteristics which are at least to some degree different from its individual components. Nanocomposite materials are composed of different materials of which at least one has nanoscale dimensions. Common types of nanocomposites consist of a combination of two different elements, with a nanoparticle that is linked to, or surrounded by, another organic or inorganic material, for example in a core-shell or heterostructure configuration. A general family of nanoparticle composites concerns the coating of a nanoscale material by a polymer, SiO2 or carbon. Other materials, such as graphene or graphene oxide (GO), are used as supports forming composites when nanoscale materials are deposited onto them. In this Review we focus on magnetic nanocomposites, describing their synthetic methods, physical properties and applications. Several types of nanocomposites are presented, according to their composition, morphology or surface functionalization. Their applications are largely due to the synergistic effects that appear thanks to the co-existence of two different materials and to their interface, resulting in properties often better than those of their single-phase components. Applications discussed concern magnetically separable catalysts, water treatment, diagnostics-sensing and biomedicine.

Comparative study of arsenic removal by iron-based nanomaterials: Potential candidates for field applications

Graphene oxide supported magnetite (GM) and graphene oxide supported nanoscale zero-valent iron (GNZVI) nanohybrids were compared for arsenic removal at a wide pH range (3-9). While already published work reported high process efficiency for GM and GNZVI, they cannot be compared one-on-one given the non-identical experimental conditions. Each researcher team used different initial arsenic concentration, solution pH, and adsorbent dose. This study evaluated GM and GNZVI, bare magnetite (M), and bare nanoscale zero-valent iron (NZVI) for aqueous arsenic removal under similar experimental conditions. GNZVI worked more efficiently (>90%) in a wide pH range (3-9) for both As(III) and As(V), while GM was efficient (>90%) only at pH 3 for As(V) and As(III) removal was maximum of ~80% at pH 9. GNZVI also exhibited better aqueous dispersibility with a zeta potential of -21.02 mV compared to other adsorbents in this experiment. The arsenic removal based on normalized iron content indicated that the nanohybrids recorded improved arsenic removal compare to bare nanoparticles, and GNZVI worked the best. In NZVI-based nanomaterials (GNZVI and NZVI), electrostatic attraction played a limited role while surface complexation was dominant in removal of both the arsenic species. In case of M-based nanomaterials (GM and M), As(V) removal was controlled by electrostatic attraction while As(III) adsorption was ligand exchange and surface complexation. GNZVI has the potential for field application for drinking water arsenic removal.

Arsenic Contamination of Groundwater and Its Implications for Drinking Water Quality and Human Health in Under-Developed Countries and Remote Communities—A Review

Arsenic is present naturally in many geological formations around the world and has been found to be a major source of contamination of groundwater in some countries. This form of contamination represents a serious threat to health, economic and social well-being, particularly in under-developed countries and remote communities. The chemistry of arsenic and the factors that influence the form(s) in which it may be present and its fate when introduced into the environment is discussed briefly in this review. A global overview of arsenic contamination of groundwater around the world is then discussed. As a case study, the identified and established causes of groundwater contamination by arsenic in Bangladesh is highlighted and a perspective is provided on the consequential health, agricultural, social and economic impacts. In addition, the relevant removal strategies that have been developed and can generally be used to remediate arsenic contamination are discussed. Also, the possible influence of groundwater inorganic compositions, particularly iron and phosphate, on the effectiveness of arsenic removal is discussed. Furthermore, some specific examples of the filter systems developed successfully for domestic arsenic removal from groundwater to provide required potable water for human consumption are discussed. Lastly, important considerations for further improving the performance and effectiveness of these filter systems for domestic use are outlined.

Kinetic and Isotherm Study of As(III) Removal from Aqueous Solution by PET Track-Etched Membranes Loaded with Copper Microtubes

This paper reports on the synthesis and structure elucidation of track-etched membranes (TeMs) with electrolessly deposited copper microtubes (prepared in etched-only and oxidized polyethylene terephthalate (PET) TeMs), as well as on the comparative testing of arsenic (III) ion removal capacities through bath adsorption experiments. The structure and composition of composites were investigated by X-ray diffraction technique and scanning electron and atomic force microscopies. It was determined that adsorption followed pseudo-second-order kinetics, and the adsorption rate constants were calculated. A comparative study of the applicability of the adsorption models of Langmuir, Freundlich, and Dubinin-Radushkevich was carried out in order to describe the experimental isotherms of the prepared composite TeMs. The constants and parameters of all of the above equations were determined. By comparing the regression coefficients R2, it was shown that the Freundlich model describes the experimental data on the adsorption of arsenic through the studied samples better than others. Free energy of As(III) adsorption on the samples was determined using the Dubinin-Radushkevich isotherm model and was found to be 17.2 and 31.6 kJ/mol for Cu/PET and Cu/Ox_PET samples, respectively. The high EDr value observed for the Cu/Ox_PET composite indicates that the interaction between the adsorbate and the composite is based on chemisorption.

Euler’s Numerical Method for Ions Rejection Reassessment of a Defect-Free Synthesized Nanofiltration Membrane with Ultrathin Titania Film as the Selective Layer

Titanium (Ti) nanoparticles (NPs) were successfully seeded on the platform of a polyacrylonitrile (PAN) ultrafiltration (UF) membrane previously coated with bio-glue (a co-deposition of dopamine hydrochloric bicarbonate buffer having undergone pyrocatechol deprotonation). The tools in vogue, especially field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and atomic force microscopy (AFM), have made it possible to fully characterize the structure of the new organic-inorganic nanofiltration (NF) membrane, namely NF_PAN_Ti. A soft computing model has been applied to make commonplace the complex and implicit extended Nernst–Planck equations that govern the transport of ions through NF membranes. Euler’s numerical method was applied with a small step-size and the results obtained were very interesting. The filtration velocity approach of GUEROUT-ELFORD-FERRY helped to estimate the average pore size of NF_PAN_Ti to rp = 0.538 nm. A six-day test carried out on NF_PAN_Ti demonstrated its long-term stability and showed a steady-rejection rate of 89.3% of MgCl2 salt and permeate flux of 56 L·m−2·h−1. The Euler’ numerical method corroborated perfectly the experimental findings since the relative error was found to be very low at 0.33% for Cl− and 0.09% for Mg2+ (RE << 0.1). These practical prediction tools may henceforth help in the choice and calibration of next-generation NF membranes’ synthesis.

Enhanced Photocatalytic Activity of ZnO-Graphene Oxide Nanocomposite by Electron Scavenging

Advances in nanotechnology have opened new doors to overcome the problems related to contaminated water by introducing photocatalytic nanomaterials. These materials can effectively degrade toxic contaminants, such as dyes and other organic pollutants, into harmless by-products such as carbon dioxide and water. Consequently, these photocatalytic nanomaterials have the potential to provide low-cost and environment-friendly alternatives to conventional water and wastewater treatment techniques. In this study, a nanocomposite of zinc oxide and graphene oxide was developed and evaluated for photocatalysis. This nanocomposite was characterized by XRD, FTIR, FESEM, Diffuse Reflectance Spectroscopy (DRS), TEM and UV-Vis spectrophotometer. The photocatalytic behavior of the nanocomposite was studied through the degradation of methyl orange under ultraviolet light. It is reported that the weight ratios of zinc oxide and graphene oxide do not considerably affect the photocatalytic performance, which gives this process more compositional flexibility. Moreover, hydrogen peroxide was used as an electron scavenger to increase the time-efficiency of the process. The photodegradation rate can be significantly improved (up to 24 times) with the addition of hydrogen peroxide, which increases the number of trapped electrons and generates more oxidizing species, consequently increasing the reaction rate.

A critical review on recent developments in MOF adsorbents for the elimination of toxic heavy metals from aqueous solutions

Effective and substantial remediation of contaminants especially heavy metals from water is still a big challenge in terms of both environmental and biological perspectives because of their adverse effects on the human health. Many techniques including adsorption, ion exchange, co-precipitation, chemical reduction, ultrafiltration, etc. are reported for eliminating heavy metal ions from the water. However, adsorption has preferred because of its simple and easy handlings. Several types of adsorbents are observed and documented well for the purpose. Recently, highly porous metal-organic frameworks (MOFs) were developed by incorporating metals and organic ligands together and claimed as potent adsorbents for the remediation of highly toxic heavy metals from the aqueous solutions due to their unique features like greater surface area, high chemical stability, green and reuse material, etc. In this review, the authors discussed systematically some recent developments about secure MOFs to eliminate the toxic metals such as arsenic (both arsenite and arsenate), chromium(VI), cadmium (Cd), mercury (Hg) and lead (Pb). MOFs are observed as the most efficient adsorbents with greater selectivity as well as high adsorption capacity for metallic contamination. Graphical abstract.

Cu/CuO Composite Track-Etched Membranes for Catalytic Decomposition of Nitrophenols and Removal of As(III)

One of the promising applications of nanomaterials is to use them as catalysts and sorbents to remove toxic pollutants such as nitroaromatic compounds and heavy metal ions for environmental protection. This work reports the synthesis of Cu/CuO-deposited composite track-etched membranes through low-temperature annealing and their application in catalysis and sorption. The synthesized Cu/CuO/poly(ethylene terephthalate) (PET) composites presented efficient catalytic activity with high conversion yield in the reduction of nitro aryl compounds to their corresponding amino derivatives. It has been found that increasing the time of annealing raises the ratio of the copper(II) oxide (CuO) tenorite phase in the structure, which leads to a significant increase in the catalytic activity of the composites. The samples presented maximum catalytic activity after 5 h of annealing, where the ratio of CuO phase and the degree of crystallinity were 64.3% and 62.7%, respectively. The catalytic activity of pristine and annealed composites was tested in the reduction of 4-nitroaniline and was shown to remain practically unchanged for five consecutive test cycles. Composites annealed at 140 °C were also tested for their capacity to absorb arsenic(III) ions in cross-flow mode. It was observed that the sorption capacity of composite membranes increased by 48.7% compared to the pristine sample and reached its maximum after 10 h of annealing, then gradually decreased by 24% with further annealing.

Nanofiltration for Arsenic Removal: Challenges, Recent Developments, and Perspectives

Arsenic (As) removal is of major significance because inorganic arsenic is highly toxic to all life forms, is a confirmed carcinogen, and is of significant environmental concern. As contamination in drinking water alone threatens more than 150 million people all over the world. Therefore, several conventional methods such as oxidation, coagulation, adsorption, etc., have been implemented for As removal, but due to their cost-maintenance limitations; there is a drive for advanced, low cost nanofiltration membrane-based technology. Thus, in order to address the increasing demand of fresh and drinking water, this review focuses on advanced nanofiltration (NF) strategy for As removal to safeguard water security. The review concentrates on different types of NF membranes, membrane fabrication processes, and their mechanism and efficiency of performance for removing As from contaminated water. The article provides an overview of the current status of polymer-, polymer composite-, and polymer nanocomposite-based NF membranes, to assess the status of nanomaterial-facilitated NF membranes and to incite progress in this area. Finally, future perspectives and future trends are highlighted.

Poly (amidoamine) generation 6 functionalized Fe3O4@SiO2/GPTMS core-shell magnetic NPs as a new adsorbent for Arsenite adsorption: kinetic, isotherm and thermodynamic studies

In this survey a new route has been developed the preparation of poly (amidoamine) generation 6 (PAMAM-G6) dendrimer functionalized Fe3O4/SiO2 nanoparticle and was used for arsenite (As (III)) adsorption. SiO2 was first grafted onto the surface of Fe3O4 to formation a core-shell structure. Then the introduction of epoxy rings were done by hydrolysis of methylsilane groups of 3-Glycidoxypropyltrimethoxysilane (GPTMS) on OH groups of SiO2 and afterwards, PAMAM-G6 reacted with epoxy rings of GPTMS to obtain a multiamino magnetic adsorbent. The as-prepared nanocomposite was characterized by TEM, Zeta potential, FESEM, VSM, FTIR, Raman and XPS techniques. The effects of reaction time from 5 to 50 min, initial As (III) concentration in the range of 1-10 mgL-1, initial adsorbent concentration in the range of 10-50 mgL-1 and initial pH in the range 3-8 were studied. The resulting of kinetic and isotherm models displays high adsorption affinity (233 mg/g) for As (III) and the adsorbent can reach the adsorbent can reach the adsorption equilibrium at a neutral pH (7). The As (III) loaded nanocomposite could be separated readily from aqueous solution by magnetic and regenerated simply via NaOH. The study of the adsorption procedure showed that the pseudo-second order kinetics and Langmuir isotherm well-fitted with the experimental data of As (III) adsorption onto nanocomposite.

A review on exploration of Fe2O3 photocatalyst towards degradation of dyes and organic contaminants

Photocatalytic degradation is among the promising technology for removal of various dyes and organic contaminants from environment owing to its excellent catalytic activity, low energy utilization, and low cost. As one of potential photocatalysts, Fe₂O₃ has emerged as an important material for degradation of numerous dyes and organic contaminants caused by its tolerable band gap, wide harvesting of visible light, good stability and recyclability. The present review thoroughly summarized the classification, synthesis route of Fe₂O₃ with different morphologies, and several modifications of Fe₂O₃ for improved photocatalytic performance. These include the incorporation with supporting materials, formation of heterojunction with other semiconductor photocatalysts, as well as the fabrication of Z-scheme. Explicitly, the other photocatalytic applications of Fe₂O₃, including for removal of heavy metals, reduction of CO₂, evolution of H₂, and N₂ fixation are also deliberately discussed to further highlight the huge potential of this catalyst. Moreover, the prospects and future challenges are also comprised to expose the unscrutinized criteria of Fe₂O₃ photocatalyst. This review aims to contribute a knowledge transfer for providing more information on the potential of Fe₂O₃ photocatalyst. In the meantime, it might give an idea for utilization of this photocatalyst in other environmental remediation application.

Novel nanostructured iron oxide cryogels for arsenic (As(III)) removal

Novel macroporous iron oxide nanocomposite cryogels were synthesized and assessed as arsenite (As(III)) adsorbents. The two-step synthesis method, by which a porous nanonetwork of iron oxide is firstly formed, allowed a homogeneous dispersion of the iron oxide in the cryogel reaction mixture, regardless of the nature of the co-polymer forming the cryogel structure. The cryogels showed excellent mechanical properties, especially the acrylamide-based cryogel. This gel showed the highest As(III) adsorption capacity, with the maximum value estimated at 118 mg/g using the Langmuir model. The immobilization of the nanostructured iron oxide gel into the cryogel matrix resulted in slower adsorption kinetics, however the cryogels offer the advantage of a stable three-dimensional structure that impedes the release of the iron oxide nanoparticles into the treated effluent. A preliminary toxicity evaluation of the cryogels did not indicate any apparent inhibition of human hepatic cells activity, which together with their mechanical stability and high adsorption capacity for As(III) make them excellent materials for the development of nanoparticle based adsorption devices for drinking water treatment.

Arsenic Removal from Water by Green Synthesized Magnetic Nanoparticles

Magnetite nanoparticles were synthesized by a simple and ecofriendly method using onion peel (MNp-OP) and corn silk extract (MNp-CS), in order to develop new low-cost adsorbents for arsenic removal from groundwater. As a point of comparison, magnetite nanoparticles were also synthesized with a conventional chemical process (MNp-CO). The antioxidant potential of onion peel and corn silk extracts was determined using ferric reducing antioxidant power (FRAP) and free radical (DPPH) scavenging assays, including the total phenolics, flavonoids and tannins contents. The synthesized magnetite nanoparticles were characterised using different techniques (Scanning electron microscope/Energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET) surface area analyzer). The adsorption capacity of MNp-OP and MNp-CS and the arsenic removal mechanism of these novel adsorbents was investigated through kinetic and equilibrium experiments and their corresponding mathematical models. Characterisation of MNp-OP and MNp-CS shows high BET specific surface areas of 243 m2/g and 261 m2/g, respectively. XRD and FTIR analysis confirmed the formation and presence of magnetite nanoparticles. The arsenic adsorption mechanism on MNp-OP, MNp-CS and MNp-CO involves chemisorption, intraparticle and external diffusion. Maximal adsorption capacities of MNp-OP, MNp-CS and MNp-CO were 1.86, 2.79, and 1.30 mg/g respectively. The green synthesis applied using onion peel and corn silk extracts was cost effective and environmentally friendly, and results in adsorbents with a high capacity for arsenic and magnetic properties, making them a very promising alternative approach in the treatment of arsenic contaminated groundwater.

Differently shaped nanocrystalline (Fe, Y)3O4 and its adsorption efficiency toward inorganic arsenic species

Herein we report effects of partial substitution of Fe³⁺ by Y³⁺ in magnetite (Fe₃O₄) on morphology and inorganic arsenic species adsorption efficiency of the Fe_3-x Y _x O₄ nanoparticles formed. The series of Fe_3-x Y _x O₄ (x = 0.00, 0.042 and 0.084, labeled as Y00, Y05 and Y10, respectively) was synthesized using co-precipitation followed by microwave-hydrothermal treatment (MW) at 200 °C. With increase of yttrium content (x value), both the morphological inhomogeneity of the samples and the fraction of spinel nanorods as compared to spinel pseudospherical particles increased. By both transmission electron microscopy and x-ray powder diffraction analyses, it was determined that the direction of growth of the spinel nanorods is along the [110] crystallographic direction. The Fe_3-x Y _x O₄ affinities of adsorption toward the inorganic arsenic species, As(III) (arsenite, AsO₃ ^3-) and As(V) (arsenate, AsO₄ ^3-), were investigated. Increased Y³⁺ content related to changes in sample morphology was followed by a decrease of As(III) removal efficiency and vice versa for As(V). The increase in Y³⁺ content, in addition to increasing the adsorption capacity for As(V), significantly expanded the optimum pH range for the maximum removal and decreased the contact time for necessary 50% removal (t _1/2) of As(V) (Y00: pH 2-3, t _1/2 = 3.12 min; Y05: pH 2-6, t _1/2 = 2.12 min and Y10: pH 2-10, t _1/2 = 1.12 min). The results point to incorporation of Y³⁺ in the crystal lattice of magnetite, inducing nanorod spinel structure formation with significant changes in sorption properties important for the removal of inorganic arsenic from waters.

Titanium-based nanocomposite materials for arsenic removal from water: A review

Arsenic is highly carcinogenic element and less concentration of this chemical element makes natural water unsafe for human consumption. Versatile techniques including adsorption method have been established to remove the arsenic from water. However, adsorption is found to be one of effective method for the remediation of arsenic from contaminated water. Different types of natural adsorbents i.e. clays, waste materials, carbon based material have been studied widely for the adsorption of arsenic. Recently, nanotechnology is considered to be one of the best technology for waste water treatment. Therefore researchers have synthesized several types of nanoadsorbents and investigated them for the removal of various pollutants including arsenic from water. Now days, attention is paid on development of nanocomposite materials which are proven as competent arsenic adsorbent candidate as compared to other adsorbents due to dominant structural and surface features. Various metal/metal oxide based nanocomposites have been developed and studied for arsenic removal from aqueous media. It has been reported that TiO₂ based nanocomposite exhibit stong affinity for both inorganic form of arsenic. Therefore, in this review numerous metal or metal oxide based titania nanocomposites i.e. TiO₂-αFe₂O₃, NHITO, Ce-Ti oxide, Zr-TiO_2, RGO-MFT etc. have been discussed in details for the water treatment containing arsenic. This review also presents an overview of low cost adsorbents, titania based nanoadsorbent and hybrid titania nanostructures for the removal of arsenic. In this review paper the particle size, surface area and adsorption efficiency of these titania based materials at different pH are also been presented in tabulated form. It provides the opportunity to choose best titania based nanocomposites for the treatment of arsenic polluted water.

Well-dispersed TiO2 nanoparticles anchored on Fe3O4 magnetic nanosheets for efficient arsenic removal

Magnetic iron-titanium binary oxide as an effective adsorbent for arsenic contaminant is a challenge primarily because of their bulk structure and agglomeration effect. Herein, a novel and uniform sandwich-like magnetic Fe₃O₄@TiO₂ sheets were synthesized by utilizing a facile strategy involving amorphous-to-crystalline transformation and reduction in H₂, to achieve dispersed anatase TiO₂ nanoparticles with a small size of ∼8 nm anchored on Fe₃O₄ sheets. The resultant Fe₃O₄@TiO₂ sheets nanocomposite possessing a high specific surface area of ∼89.4 m² g^-1 and available magnetic susceptibility of ∼20.0 emu g^-1, significantly enhanced the photocatalytic oxidation property of arsenite and considerable adsorption capability for arsenic removal. The adsorption capacities of As(V) and As(III) with UV-assisted from adsorption experimental results were 36.36 and 30.96 mg g^-1, respectively, while the residual concentrations for both As(V) and As(III) were lower than the strict limit of 10 μg L^-1. Adsorption equilibriums were almost reached within 45 min. In addition, the adsorbent exhibited excellent stability over a broad pH range of 3-9 and still maintained great removal efficiency after five time regeneration cycles. Furthermore, except for silicate and phosphate, the extremely weak inhibiting influences of common co-existing ions in arsenic removal process, demonstrated that the developed magnetic Fe₃O₄@TiO₂ sheets with unique nanostructure could be a promising efficient adsorbent for arsenic removal.

A critical review on arsenic removal from water using iron-based adsorbents

Intensive research efforts have been pursued to remove arsenic (As) contamination from water with an intention to provide potable water to millions of people living in different countries. Recent studies have revealed that iron-based adsorbents, which are non-toxic, low cost, and easily accessible in large quantities, offer promising results for arsenic removal from water. This review is focused on the removal of arsenic from water using iron-based materials such as iron-based nanoparticles, iron-based layered double hydroxides (LDHs), zero-valent iron (ZVI), iron-doped activated carbon, iron-doped polymer/biomass materials, iron-doped inorganic minerals, and iron-containing combined metal oxides. This review also discusses readily available low-cost adsorbents such as natural cellulose materials, bio-wastes, and soils enriched with iron. Details on mathematical models dealing with adsorption, including thermodynamics, kinetics, and mass transfer process, are also discussed. For elucidating the adsorption mechanisms of specific adsorption of arsenic on the iron-based adsorbent, X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) are frequently used. Overall, iron-based adsorbents offer significant potential towards developing adsorbents for arsenic removal from water.

Effective removal of heavy metals by nanosized hydrous zirconia composite hydrogel and adsorption behavior study

A novel type of adsorbent, hydrous zirconium oxide (HZO) based on polymer hydrogel (HZO-P(TAA/HEA) hydrogel), was synthesized by irradiation polymerization and in situ precipitation methods to remove heavy metals from water efficiently. The composite hydrogel was characterized using scanning electron microscope (SEM), transmission electron microscope (TEM), swelling kinetics, zeta potential, X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS). The results indicated that HZO nanoparticles were stably loaded on the P(TAA/HEA) hydrogel, swelling properties, and thermal stability were also enhanced after the loading of HZO. Besides, the batch adsorption experiments revealed that adsorption time, pH, initial concentration of heavy metals, and coexisting ions influenced the adsorption process significantly. The adsorption capacities of HZO-P(TAA/HEA) hydrogel for Pb²⁺, Cu²⁺, Cd²⁺, and Ni²⁺ was 0.620 mmol g^-1, 0.615 mmol g^-1, 0.701 mmol g^-1, and 0.700 mmol g^-1, respectively. The adsorption isotherms fitted Langmuir equation well, and the adsorption kinetics followed second-order kinetics; it was manifested that the priority of competitive adsorption followed the order: Pb²⁺ > Cu²⁺ > Ni²⁺ > Cd²⁺. Furthermore, based on the analysis results of FTIR and XPS, the adsorption mechanism could mainly be the complexation between hydrous zirconia and heavy metals. The results indicate that nanocomposite HZO-P(TAA/HEA) hydrogel is a promising heavy metal adsorbent.

Enhancing adsorption capacity while maintaining specific recognition performance of mesoporous silica: a novel imprinting strategy with amphiphilic ionic liquid as surfactant

In order to facilitate the broad applications of molecular recognition materials in biomedical areas, it is critical to enhance their adsorption capacity while maintaining their excellent recognition performance. In this work, we designed and synthesized well-defined peptide-imprinted mesoporous silica (PIMS) for specific recognition of an immunostimulating hexapeptide from human casein (IHHC) by using amphiphilic ionic liquid as the surfactant to anchor IHHC via a combination of one-step sol-gel method and docking oriented imprinting approach. Thereinto, theoretical calculation was employed to reveal the multiple binding interactions and dual-template configuration between amphiphilic ionic liquid and IHHC. The fabricated PIMS was characterized and an in-depth analysis of specific recognition mechanism was conducted. Results revealed that both adsorption and recognition capabilities of PIMS far exceeded that of the NIMS's. More significantly, the PIMS exhibited a superior binding capacity (60.5 mg g^-1), which could increase 18.9% than the previous work. The corresponding imprinting factor and selectivity coefficient could reach up to 4.51 and 3.30, respectively. The PIMS also possessed lickety-split kinetic binding for IHHC, where the equilibrium time was only 10 min. All of these merits were due to the high surface area and the synergistic effect of multiple interactions (including hydrogen bonding, π-π stacking, ion-ion electrostatic interactions and van der Waals interactions, etc) between PIMS and IHHC in imprinted sites. The present work suggests the potential application of PIMS for large-scale and high-effective separation of IHHC, which may lead to their broad applications in drug/gene deliver, biosensors, catalyst and so on.

Arsenic removal from water by metal-organic framework MIL-88A microrods

Fe-based metal-organic framework MIL-88A microrods were synthesized by hydrothermal method, which were used to adsorb As(V) in water for the first time. The experimental results indicated that MIL-88A has a very fast adsorption rate towards arsenic in water. The kinetic and isothermal data for arsenic removal were better fitted to the pseudo-second-order kinetic model and Langmuir model, respectively, implying a chemical and monolayer adsorption for As(V) on MIL-88A microrods. Two rate-controlling processes during adsorption were revealed by the intraparticle diffusion model. The maximum adsorption capacity of MIL-88A reached 145 mg g^-1, higher than those of Fe-based MIL adsorbents reported previously, which probably originates from its unique microstructure with abundant OH^- groups and an unusual large swelling towards water. These show that Fe-based MIL-88A is a good candidate for arsenic removal.

Identification of Fe and Zr oxide phases in an iron-zirconium binary oxide and arsenate complexes adsorbed onto their surfaces

The Fe-Zr binary oxide adsorbents have higher arsenic adsorptive capacities than either iron oxide or zirconium oxide alone, indicating a strong synergistic effect exists between Fe and Zr oxides. However, no generally accepted in-depth explanations have been reached on the origin of this better performance. In the present study, the component phases, the active surface sites, the structure of the adsorbed As(V) surface species, and the mechanism of the synergistic effect, were investigated and elucidated using multiple advanced experimental techniques combined with quantum chemical calculations. Goethite and lepidocrocite were identified as the main Fe oxide components while amorphous zirconium hydroxide was the main Zr oxide component, respectively. A monodentate-mononuclear complex and a bidentate-binuclear complex were revealed to be dominant on the surface, respectively, when at lower and higher initial As(V) concentrations. Density functional theory calculations indicated that As(V) preferred to bind with Zr-OH rather than Fe-OH. This was verified with the As K-edge EXAFS results and XPS observations. The synergistic effect was due to a short-range ordering state, the enlarged contents of amorphous and poorly-crystalline fractions, and increased hydroxyl surface site density. These results lead to the realization that the above properties are preferred in future adsorbent preparations.

Arsenic removal by periphytic biofilm and its application combined with biochar

A biochar and periphyton-based system (BPS) comprising of a biochar column and a periphyton bioreactor was designed to avoid the toxicity issue associated with removing As(III) from wastewater. Results showed that the periphyton can grow when As(III) is less than 5.0mgL^-1. The BPS obtained a high As(III) removal rate (∼90.2-95.4%) at flow rate=1.0mLmin^-1 and initial concentration of As(III)=2.0mgL^-1. About 60% of the As(III) was pre-treated (adsorbed) in the biochar column and the removal of the remaining As(III) was attributed to the periphyton bioreactor. The As(III) removal process by periphytic biofilm in the initial stage fits a pseudo-second-kinetic model. The calcite in the periphytic biofilm surfaces and the OH and CO groups were responsible for the As(III) removal. This study indicates the feasibility of the BPS for As(III) removal in practice.

Magnetic mesoporous TiO2 microspheres for sustainable arsenate removal from acidic environments

Unique magnetic mesoporous TiO₂ microspheres exhibit superior arsenate removal performance and high stability in acidic environments.

Au Nanoclusters Sensitized Black TiO2-x Nanotubes for Enhanced Photodynamic Therapy Driven by Near-Infrared Light

The low reactive oxygen species production capability and the shallow tissue penetration of excited light (UV) are still two barriers in photodynamic therapy (PDT). Here, Au cluster anchored black anatase TiO_2-x nanotubes (abbreviated as Au₂₅ /B-TiO_2-x NTs) are synthesized by gaseous reduction of anatase TiO₂ NTs and subsequent deposition of noble metal. The Au₂₅ /B-TiO_2-x NTs with thickness of about 2 nm exhibit excellent PDT performance. The reduction process increased the density of Ti³⁺ on the surface of TiO₂ , which effectively depresses the recombination of electron and hole. Furthermore, after modification of Au₂₅ nanoclusters, the PDT efficiency is further enhanced owing to the changed electrical distribution in the composite, which forms a shallow potential well on the metal-TiO₂ interface to further hamper the recombination of electron and hole. Especially, the reduction of anatase TiO₂ can expend the light response range (UV) of TiO₂ to the visible and even near infrared (NIR) light region with high tissue penetration depth. When excited by NIR light, the nanoplatform shows markedly improved therapeutic efficacy attributed to the photocatalytic synergistic effect, and promotes separation or restrained recombination of electron and hole, which is verified by experimental results in vitro and in vivo.