Simultaneous photocatalytic degradation of p -cresol and Cr (VI) by metal oxides supported reduced graphene oxide

Eco-friendly sunlight driven photocatalytic remediation of water pollutants using N-doped NiO integrated into a guar gum-agar polymeric network

Hydrogel based photocatalysts with strong photocatalytic and adsorption capacities have promising future in wastewater treatment. Herein, a novel nitrogen doped NiO/guargum agar-agar nanocomposite hydrogel (GGAA@N-NiO) was synthesized via facile co-precipitation and in-situ methods. Characterization using relevant tools confirmed successful inclusion of N-NiO in the hydrogel-matrix. The higher zeta-potential of GGAA@N-NiO (-23.4) than N-NiO (-16.3) confirms the greater stability. The average crystallite size for NiO (7.82 nm) and N-NiO (4.38 nm) was calculated using the Scherrer equation and, NiO (5.7 nm) and N-NiO (2.31 nm) using WH plot. FESEM image, showed particle size of N-NiO 79.4 nm. Band gaps 2.70 eV, 2.75 eV, and 3.03 eV for GGAA@N-NiO, N-NiO, and NiO, respectively, were calculated using Kubelka Munk plots. The lower PL intensity of GGAA@N-NiO indicates a suppressed electron-hole (e-/h+) recombination rate, which reflects its enhanced photocatalytic activity. GGAA@N-NiO achieved 95.3 % removal of benzyl butyl phthalate (BBP) and 94.6 % removal of para-cresol (PC) within 240 min under optimized conditions (i.e. pH ∼7.0; catalyst-dose: 1.5 g/L with BBP and 1.0 g/L with PC, pollutant-concentration: 20 ppm for BBP and, 50 ppm for PC). The removal followed first-order-kinetics and Langmuir-isotherm, with ·OH radicals exhibiting a dominant role in the photocatalytic-removal process. GC-MS analysis confirmed the degradation of BBP and PC into safer metabolites. The nanocomposite was reusable over six cycles, demonstrating stability. This study offers cost-effective and highly-efficient approach to developing stable hydrogel-supported photocatalysts for water-remediation.

Emerging micropollutants in aquatic ecosystems and nanotechnology-based removal alternatives: A review

There is a significant concern about the accessibility of uncontaminated and safe drinking water, a fundamental necessity for human beings. This concern is attributed to the toxic micropollutants from several emission sources, including industrial toxins, agricultural runoff, wastewater discharges, sewer overflows, landfills, algal blooms and microbiota. Emerging micropollutants (EMs) encompass a broad spectrum of compounds, including pharmaceutically active chemicals, personal care products, pesticides, industrial chemicals, steroid hormones, toxic nanomaterials, microplastics, heavy metals, and microorganisms. The pervasive and enduring nature of EMs has resulted in a detrimental impact on global urban water systems. Of late, these contaminants are receiving more attention due to their inherent potential to generate environmental toxicity and adverse health effects on humans and aquatic life. Although little progress has been made in discovering removal methodologies for EMs, a basic categorization procedure is required to identify and restrict the EMs to tackle the problem of these emerging contaminants. The present review paper provides a crude classification of EMs and their associated negative impact on aquatic life. Furthermore, it delves into various nanotechnology-based approaches as effective solutions to address the challenge of removing EMs from water, thereby ensuring potable drinking water. To conclude, this review paper addresses the challenges associated with the commercialization of nanomaterial, such as toxicity, high cost, inadequate government policies, and incompatibility with the present water purification system and recommends crucial directions for further research that should be pursued.

Toward Efficient Bactericidal and Dye Degradation Performance of Strontium- and Starch-Doped Fe2O3 Nanostructures: In Silico Molecular Docking Studies

In this study, various concentrations of strontium (Sr) into a fixed amount of starch (St) and Fe2O3 nanostructures (NSs) were synthesized with the co-precipitation approach to evaluate the antibacterial and photocatalytic properties of the concerned NSs. The study aimed to synthesize nanorods of Fe2O3 with co-precipitation to enhance the bactericidal behavior with dopant-dependent Fe2O3. Advanced techniques were utilized to investigate the structural characteristics, morphological properties, optical absorption and emission, and elemental composition properties of synthesized samples. Measurements via X-ray diffraction confirmed the rhombohedral structure for Fe2O3. Fourier-transform infrared analysis explored the vibrational and rotational modes of the O-H functional group and the C=C and Fe-O functional groups. The energy band gap of the synthesized samples was observed in the range of 2.78-3.15 eV, which indicates that the blue shift in the absorption spectra of Fe2O3 and Sr/St-Fe2O3 was identified with UV-vis spectroscopy. The emission spectra were obtained through photoluminescence spectroscopy, and the elements in the materials were determined using energy-dispersive X-ray spectroscopy analysis. High-resolution transmission electron microscopy micrographs showed NSs that exhibit nanorods (NRs), and upon doping, agglomeration of NRs and nanoparticles was observed. Efficient degradations of methylene blue increased the photocatalytic activity in the implantation of Sr/St on Fe2O3 NRs. The antibacterial potential for Escherichia coli and Staphylococcus aureus was measured against ciprofloxacin. E. coli bacteria exhibit inhibition zones of 3.55 and 4.60 mm at low and high doses, respectively. S. aureus shows the measurement of inhibition zones for low and high doses of prepared samples at 0.47 and 2.40 mm, respectively. The prepared nanocatalyst showed remarkable antibacterial action against E. coli bacteria rather than S. aureus at high and low doses compared to ciprofloxacin. The best-docked conformation of the dihydrofolate reductase enzyme against E. coli for Sr/St-Fe2O3 showed H-bonding interactions with Ile-94, Tyr-100, Tyr-111, Trp-30, ASP-27, Thr-113, and Ala-6.

Highly Selective Room Temperature Detection of NH3 and NOx Using Oxygen-Deficient W18O49-Supported WS2 Heterojunctions

In this paper, we reported the controlled synthesis of tungsten disulfide/reduced tungsten oxide (WS₂/W₁₈O₄₉) heterojunctions for highly efficient room temperature NO_x and ammonia (NH₃) sensors. X-ray diffraction analysis revealed the formation of the oxygen-deficient W₁₈O₄₉ phase along with WS₂. Field-emission scanning electron microscopy and transmission electron microscopy displayed the formation of WS₂ flakes over W₁₈O₄₉ nanorods. X-ray photoelectron spectroscopy showed the presence of tungsten in W⁴⁺, W⁵⁺, and W⁶⁺ oxidation states corresponding to WS₂ and W₁₈O₄₉, respectively. The WS₂/W₁₈O₄₉ heterojunction sensor exhibited sub-ppm level sensitivity to NO_x and NH₃ at room temperature. The heterojunction sensor detected 0.6 ppm NO_x and 0.5 ppm NH₃, with a corresponding response of 7.1 and 3.8%, respectively. The limit of detection of the sensor was calculated to be 0.05 and 0.17 ppm for NH₃ and NO_x, respectively. The cyclic stability test showed that the sensor exhibited high stability even after 24 cycles for the detection of NH₃ and 14 cycles for NO_x. Compared to pristine WO₃ and WS₂, the WS₂/W₁₈O₄₉ heterojunction showed high selectivity toward NO_x and NH₃. The results could be useful for the development of room temperature NO_x and NH₃ sensors.

Saiz P, Reizabal A, Wuttke S, Celaya-Azcoaga L, Valverde A, Fernández de Luis R. A State-of-the-Art of Metal-Organic Frameworks for Chromium Photoreduction vs. Photocatalytic Water Remediation

Hexavalent chromium (Cr(VI)) is a highly mobile cancerogenic and teratogenic heavy metal ion. Among the varied technologies applied today to address chromium water pollution, photocatalysis offers a rapid reduction of Cr(VI) to the less toxic Cr(III). In contrast to classic photocatalysts, Metal-Organic frameworks (MOFs) are porous semiconductors that can couple the Cr(VI) to Cr(III) photoreduction to the chromium species immobilization. In this minireview, we wish to discuss and analyze the state-of-the-art of MOFs for Cr(VI) detoxification and contextualizing it to the most recent advances and strategies of MOFs for photocatalysis purposes. The minireview has been structured in three sections: (i) a detailed discussion of the specific experimental techniques employed to characterize MOF photocatalysts, (ii) a description and identification of the key characteristics of MOFs for Cr(VI) photoreduction, and (iii) an outlook and perspective section in order to identify future trends.

Pyridazine doped g-C3N4 with nitrogen defects and spongy structure for efficient tetracycline photodegradation and photocatalytic H2 evolution

In this study, with thiourea and 3-aminopyridazine as precursors, the graphite-phase carbon nitride (ACN-x) with nitrogen defects and sponge structure is prepared via the introduction of the benzene-like ring structure of pyridazine replacing a "melem" group through hydrothermal procedure combined with calcination. It is made possible by the attraction of three hydrogen bond receptors for 3-aminopyrazine to lone pair electrons on the "melem" molecule. The remarkable extensively photocatalytic activity can be attributed to three effects of the introduction of 3-aminopyridazine: (i)formation of nitrogen defects between adjacent tri-s-triazine groups; (ii)formation of effective charge transfer channels within the tri-s-triazine group; (iii)the spongy structure exposed abundant amino groups(-NH₃) at edge sites, combining with the internal amino group and as hole stabilizer to prolong the excited state life of photocatalyst. The photogenerated carrier migration and separation efficiency improved effectively through the tuning synergy. As a result, ACN-x exhibits excellent photocatalytic activity, with hydrogen production efficiency of up to 11331.74 μmol g^-1 h^-1, which is approximately 94.5 times that of the pristine g-C₃N₄ (119.88 μmol g^-1 h^-1). The degradation constants of TC and RhB are 0.0498min^-1 and 0.129min^-1, which are 3.32 and 6.35 times of the pristine g-C₃N₄, respectively. The TC degradation in different initial concentrations, pH, dissolved organic matter concentrations, and water sources is conducted to prove the environmental adaptability of the ACN-x system. The mechanism of the system indicates that ·O₂^- plays an important role, and the ·OH and h⁺ play a minor role in the TC photocatalytic degradation. Finally, the TC degradation possible pathway is proposed.

Integrated p-n Junctions for Efficient Solar Water Splitting upon TiO2/CdS/BiSbS3 Ternary Hybrids for Improved Hydrogen Evolution and Mechanistic Insights

The development of efficient and novel p-n heterojunctions for photoelectrochemical (PEC) water splitting is still a challenging problem. We have demonstrated the complementary nature of (p-type) BiSbS3 as a sensitizer when coupled with (n-type) TiO2/CdS to improve the photocatalytic activity and solar to hydrogen conversion efficiency. The as-prepared p-n heterojunction TiO2/CdS/BiSbS3 exhibits good visible light harvesting capacity and high charge separation over the binary heterojunction, which are confirmed by photoluminescence (PL) and electrical impedance spectroscopy (EIS). The ternary heterojunction produces higher H2 than the binary systems TiO2/CdS and TiO2/BiSbS3. This ternary heterojunction system displayed the highest photocurrent density of 5 mA·cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) in neutral conditions, and STH of 3.8% at 0.52 V vs. RHE is observed. The improved photocatalytic response was due to the favorable energy band positions of CdS and BiSbS3. This study highlights the p-n junction made up of TiO2/CdS/BiSbS3, which promises efficient charge formation, separation, and suppression of charge recombination for improved PEC water splitting efficiency. Further, no appreciable loss of activity was observed for the photoanode over 2500 s. Band alignment and interfaces mechanisms have been studied as well.

Integrated process approach for degradation of p-cresol pollutant under photocatalytic reactor using activated carbon/TiO2 nanocomposite: application in wastewater treatment

Over the years, biodegradation has been an effective technique for waste water treatment; however, it has its own limitations. In order to achieve a higher degradation efficacy, integrated processes are being focus in this area. Therefore, the present study is targeted towards the coupling of biodegradation and photocatalytic degradation of p-cresol. The biodegradation of p-cresol was performed via lab isolate Serratia marcescens ABHI001. The obtained results confirmed that ~85% degradation of p-cresol was accomplished using Serratia marcescens ABHI001 strain in 18 h. Consequently, degradation of remaining residue (remaining p-cresol concentration initially used) was also examined in a batch reactor using activated carbon-TiO₂ nanocomposite (AC/TiO₂-NC) as a catalyst under the exposure of UV radiation. The AC/TiO₂-NC was processed via sol-gel technique and characterized by various techniques, namely Brunauer-Emmett-Teller (BET), scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transformed infrared spectroscopy (FT-IR). The investigation allowed p-cresol degradation further augment up to ~96% with the help of spectrophotometer trailed by high performance liquid chromatography (HPLC). This study demonstrates that integrated process (biodegradation-photodegradation) is the cost-effective bioremediation process to overcome such kinds of pollutant issues.

Enhanced synchronous photocatalytic 4-chlorophenol degradation and Cr(VI) reduction by novel magnetic separable visible-light-driven Z-scheme CoFe2O4/P-doped BiOBr heterojunction nanocomposites

The co-existence of organic contaminants and heavy metals including 4-chlorophenol (4-CP) and Cr(VI) in aquatic system have become a challenging task in the wastewater treatment. Herein, the synchronous photocatalytic decomposition of 4-CP and Cr(VI) over new Z-scheme CoFe₂O₄/P-BiOBr heterojunction nanocomposites were revealed. In this work, the nanocomposites were successfully developed via a surfactant-free hydrothermal method. The heterojunction interface was created by decorating magnetic CoFe₂O₄ nanoparticles onto P-BiOBr nanosheets. The as-fabricated CoFe₂O₄/P-BiOBr nanocomposites substantially improved the synchronous decomposition of 4-CP and Cr(VI) compared to the single-phase component samples under visible light irradiation. Particularly, the 30-CoFe₂O₄/P-BiOBr nanocomposite displayed the best photocatalytic performance, which decomposed 95.6% 4-CP and 100% Cr(VI) within 75 min. The photocatalytic improvement was assigned to the Z-scheme heterojunction assisted charge migration between CoFe₂O₄ and P-BiOBr, and the acceleration of charge carrier separation was validated by the findings of charge dynamics measurements. The harmful 4-CP was photodegraded into smaller organics whereas the Cr(VI) was photoreduced into Cr(III) after 30-CoFe₂O₄/P-BiOBr photocatalysis, and the good recyclability of fabricated nanocomposite in photocatalytic reaction also showed promising potential for practical applications in environmental remediation. Finally, the radical quenching tests confirmed that there existed the Z-scheme path of charge migration in CoFe₂O₄/P-BiOBr nanocomposite, which was the mechanism responsible for its high photoactivity.

A review on synergistic coexisting pollutants for efficient photocatalytic reaction in wastewater remediation

With the tremendous development of the economy and industry, the pollution of water is becoming more serious due to the excessive chemical wastes that need to remove thru reduction or oxidation reactions. Simultaneous removal of dual pollutants via photocatalytic redox reaction has been tremendously explored in the last five years due to effective decontamination of pollutants compared to a single pollutants system. In a photocatalysis mechanism, the holes in the valence band can remarkably promote the oxidation of a pollutant. At the same time, photoexcited electrons are also consumed for the reduction reaction. The synergistic between the reduction and oxidation inhibits the recombination of electron-hole pairs extending their lifetime. In this review, the binary pollutants that selectively removed via photocatalysis reduction or oxidation are classified according to heavy metal-organic pollutant (HM/OP), heavy metal-heavy metal (HM/HM) and organic-organic pollutants (OP/OP). The intrinsic between the pollutants was explained in three different mechanisms including inhibition of electron-hole recombination, ligand to metal charge transfer and electrostatic attraction. Several strategies for the enhancement of this treatment method which are designation of catalysts, pH of mixed pollutants and addition of additive were discussed. This review offers a recent perspective on the development of photocatalysis system for industrial applications.

Electrochemical Detection of Ethanol in Air Using Graphene Oxide Nanosheets Combined with Au-WO3

Detection, monitoring, and analysis of ethanol are important in various fields such as health care, food industries, and safety control. In this study, we report that a solid electrolyte gas sensor based on a proton-conducting membrane is promising for detecting ethanol in air. We focused on graphene oxide (GO) as a new solid electrolyte because it shows a high proton conductivity at room temperature. GO nanosheets are synthesized by oxidation and exfoliation of expanded graphite via the Tour's method. GO membranes are fabricated by stacking GO nanosheets by vacuum filtration. To detect ethanol, Au-loaded WO3 is used as the sensing electrode due to the excellent activity of gold nanoparticles for the catalysis of organic molecules. Au-WO3 is coupled with rGO (reduced graphene oxide) to facilitate the electron transport in the electrode. Ce ions are intercalated into the GO membrane to facilitate proton transport. The sensor based on the Ce doped-GO membrane combined with Au-WO3/rGO as a sensing electrode shows good electric potential difference (ΔV) responses to ethanol in the air at room temperature. The sensor signal reaches more than 600 mV in response to ethanol at 40 ppm in air, making it possible to detect ethanol at a few ppb (parts per billion) level. The ethanol sensing mechanism was discussed in terms of the mixed-potential theory and catalysis of ethanol on Au-WO3.

Degradation of o-, m-, p-cresol isomers using ozone in the presence of V2O5-supported Mn, Fe, and Ni catalysts

Oxidative degradation of o-, m- and p-cresols using ozone in the presence of V2O5-supported metal (Mn, Fe, Ni) catalysts was studied under ambient reaction conditions. Metal (Mn, Fe, Ni) loaded V2O5 catalysts were prepared using a wet-impregnation method, thereafter, characterized, and analyzed by use of the XRD, FT-IR, SEM-EDX, TEM, and ICP-OES. Results show the effect of the amount of a metal that was loaded on the support, particularly, how it affects the resultant catalysts’ (i) crystallite size, (ii) dispersion of an active metal over the surface of a support, and (iii) catalytic activity. Mn-loaded catalysts were found to be relatively more active for the conversion of individual cresol isomers and the activity of this catalyst was significantly enhanced at a lower Mn to V2O5 ratio (2.5 wt%). Mn(2.5 %)/V2O5 catalyst led to conversions of 66.78, 71.01 and 73.68 % with o-, m-, and p-cresols respectively within 24 h of oxidation. Oxidation products were derivatized by ethanol and a few were positively detected using GC-MS. o-Tolyl acetate and 2,5-dihydroxy toluene were detected from o-cresol, m-tolyl acetate, and 2,3-dihydroxy toluene from m-cresol and p-tolyl acetate and 3,4-dihydroxy toluene from p-cresol oxidation. Dimethyl maleate and dimethyl oxalate were detected as common products in all three isomers’ oxidation.

Recent advancement in Bi5O7I-based nanocomposites for high performance photocatalysts

Bi₅O₇I belongs to the family of bismuth oxyhalides (BiOX, X = Cl, Br, I), having a unique layered structure with an internal electrostatic field that promotes the separation and transfer of photo-generated charge carriers. Interestingly, Bi₅O₇I exhibits higher thermal stability compared to its other BiOX member compounds and absorption spectrum extended to the visible region. Bi₅O₇I has demonstrated applications in diverse fields such as photocatalytic degradation of various organic pollutants, marine antifouling, etc. Unfortunately, owing to its wide band gap of ∼2.9 eV, its absorption lies mainly in the ultraviolet region, and a tiny portion of absorption lies in the visible region. Due to limited absorption, the photocatalytic performance of pure Bi₅O₇I is still facing challenges. In order to reduce the band gap and increase the light absorption capability of Bi₅O₇I, doping and formation of heterostructure strategies have been employed, which showed promising results in the photocatalytic performance. In addition, the plasmonic heterostructures of Bi₅O₇I were also developed to further boost the efficiency of Bi₅O₇I as a photocatalyst. Here, in this review article, we present such recent efforts made for the advanced development of Bi₅O₇I regarding its synthesis, properties and applications. The strategies for photocatalytic performance enhancement have been discussed in detail. Moreover, in the conclusion section, we have presented the current challenges and discussed possible prospective developments in this field.

2D–2D WO3–Bi2WO6 photocatalyst with an S-scheme heterojunction for highly efficient Cr(vi) reduction

WO3–Bi2WO6 heterostructures display outstanding photo-reduction ability for high concentration of Cr(vi) due to the formation of 2D–2D junctions and the S-scheme transfer behavior of photogenerated e–h pairs.

Simultaneous photocatalytic reduction of hexavalent chromium and oxidation of p-cresol over AgO decorated on fibrous silica zirconia

The co-existence of heavy metals and organic compounds including Cr(VI) and p-cresol (pC) in water environment becoming a challenge in the treatment processes. Herein, the synchronous photocatalytic reduction of Cr(VI) and oxidation of pC by silver oxide decorated on fibrous silica zirconia (AgO/FSZr) was reported. In this study, the catalysts were successfully developed using microemulsion and electrochemical techniques with various AgO loading (1, 5 and 10 wt%) and presented as 1, 5 and 10-AgO/FSZr. Catalytic activity was tested towards simultaneous photoredox of hexavalent chromium and p-cresol (Cr(VI)/pC) and was ranked as followed: 5-AgO/FSZr (96/78%) > 10-AgO/FSZr (87/61%) > 1-AgO/FSZr (47/24%) > FSZr (34/20%). The highest photocatalytic activity of 5-AgO/FSZr was established due to the strong interaction between FSZr and AgO and the lowest band gap energy, which resulted in less electron-hole recombination and further enhanced the photoredox activity. Cr(VI) ions act as a bridge between the positive charge of catalyst and cationic pC in pH 1 solution which can improve the photocatalytic reduction and oxidation of Cr(VI) and pC, respectively. The scavenger experiments further confirmed that the photogenerated electrons (e^-) act as the main species for Cr(VI) to be reduced to Cr(III) while holes (h⁺) and hydroxyl radicals are domain for photooxidation of pC. The 5-AgO/FSZr was stable after 5 cycles of reaction, suggesting its potential for removal of Cr(VI) and pC simultaneously in the chemical industries.

Polysaccharide-based (nano)materials for Cr(VI) removal

Chromium is a potentially poisonous and carcinogenic species, which originates from human activities and various industries such as leather, steel, iron, and electroplating industries. Chromium is present in various oxidation states, among which hexavalent chromium (Cr(VI)) is highly toxic as a natural contaminant. Therefore, chromium, particularly Cr(VI), must be eliminated from the environment, soil, and water to overcome significant problems due to its accumulation in the environment. There are different approaches such as adsorption, ion exchange, photocatalytic reduction, etc. for removing Cr(VI) from the environment. By converting Cr(VI) to Cr(III), its toxicity is reduced. Cr(III) is essential for the human diet, even in small amounts. Today, biopolymers such as alginate, cellulose, gum, pectin, starch, chitin, and chitosan have received much attention for the removal of environmental pollutants. Biopolymers, particularly polysaccharides, are very useful compounds due to their OH and NH₂ functional groups and some advantages such as biodegradability, biocompatibility, and accessibility. Therefore, they can be widely applied in catalytic applications and as efficient adsorbents for the removal of toxic compounds from the environment. This review briefly investigates the application of polysaccharide-based (nano)materials for efficient Cr(VI) removal from the environment using adsorption/reduction, photocatalytic, and chemical reduction mechanisms.

One-Step Construction of Multi-Walled CNTs Loaded with Alpha-Fe2O3 Nanoparticles for Efficient Photocatalytic Properties

The aggregation and the rapid restructuring of the photoinduced electron−hole pairs restructuring in the process of photoelectric response remains a great challenge. In this study, a kind of Multi-walled carbon nanotubes loaded Alpha-Fe₂O₃ (CNTs/α-Fe₂O₃) heterostructure composite is successfully prepared via the one-step method. Due to the synergistic effect in the as-prepared CNTs/α-Fe₂O₃, the defect sites and oxygen-containing functional groups of CNTs can dramatically improve the interface charge separation efficiency and prevent the aggregation of α-Fe₂O₃. The improved photocurrent and enhanced hole–electron separation rate in the CNTs/α-Fe₂O₃ is obtained, and the narrower band gap is measured to be 2.8 ev with intensive visible-light absorption performance. Thus, the CNTs/α-Fe₂O₃ composite serves as an excellent visible light photocatalyst and exhibits an outstanding photocatalytic activity for the cationic dye degradation of rhodamine B (RhB). This research supplies a fresh application area forα-Fe₂O₃ photocatalyst and initiates a new approach for design of high efficiency photocatalytic materials.

Coal Fly Ash Decorated with Graphene Oxide-Tungsten Oxide Nanocomposite for Rapid Removal of Pb2+ Ions and Reuse of Spent Adsorbent for Photocatalytic Degradation of Acetaminophen

Coal fly ash was decorated with a graphene oxide-tungsten oxide nanorods nanocomposite (CFA/GO/WO3NRs nanocomposite) via a hydrothermal method and applied for the remediation of lead (Pb2+ ions). The Pb2+ ion-loaded spent adsorbent (CFA/GO/WO3NRs + Pb2+ nanocomposite) was reused for the photodegradation of acetaminophen. CFA/GO/WO3NRs + Pb2+ nanocomposite displayed rapid removal of Pb2+ ions. Pseudo-second-order kinetics and the Langmuir isotherm model described the adsorption data. The adsorption capacity of the CFA/GO/WO3NRs nanocomposite was 41.51 mg/g for the removal of Pb2+ ions. Additionally, the Pb2+ ion-loaded spent adsorbent significantly influenced the degradation of acetaminophen by photocatalysis where 93% degradation was observed. It is worthy to note the reuse application of Pb2+ ion-loaded spent adsorbent as a photocatalyst, which will significantly reduce the secondary waste obtained from conventional adsorption methods.

Enhanced visible-light driven multi-photoredox Cr(VI) and p-cresol by Si and Zr interplay in fibrous silica-zirconia

Multiple contaminants including heavy metals and phenolic compounds are normally co-exist in wastewater, which caused the treatment process is rather complicated. Herein, the synergistic photoredox of Cr(VI) and p-cresol (pC) by innovative fibrous silica zirconia (FSZr) photocatalyst was reported. The high surface area of FSZr comprised of microspheres with a bicontinuous concentric lamella structure morphology consisted of silica, while its core consisted of ZrO₂ structure. The rearrangement of FSZr framework increased the crystallinity, formed Si-O-Zr bonds and narrowed the band gap of ZrO₂ for enhanced of photoredox of Cr(VI) and pC. Compared to the reaction, the photoredox efficiency of FSZr for removing Cr(VI) and pC in simultaneous system was found to be 96 % and 59 %, respectively which are higher than that in its single system owing to the efficient electron-hole charge separation. Phenolic compound with high degree of electron donating group gave beneficial effect to photoreduction of Cr(VI). Consequently, a proposed mechanism involving multi-photoredox pathway were proposed based on photoredox reaction and scavengers studies. FSZr sustained the simultaneous photoredox activities after five runs demonstrating its possibility to be use in the wastewater treatment of various pollutants.

Fabrication of copper phthalocyanine/reduced graphene oxide nanocomposites for efficient photocatalytic reduction of hexavalent chromium

Copper(II) phthalocyanine (CuPc) and non-peripheral octamethyl-substituted copper(II) phthalocyanine (N-CuMe₂Pc) were combined with reduced graphene oxide (rGO) via a precipitation method to form CuPc/rGO and N-CuMe₂Pc/rGO nanocomposites, respectively. CuPc nanorods are distributed on rGO, and N-CuMe₂Pc exists as nanorods and nanoparticles on rGO. The Cr(VI) removal ratio of N-CuMe₂Pc/rGO exposed in simulated sunlight is 99.0% with a fast photocatalytic reaction rate of 0.0320 min^-1, which is approximately 1.5 times faster than that of CuPc/rGO (0.0215 min^-1) and far surpasses that of pristine phthalocyanine and rGO. As an electron acceptor, rGO can suppress the recombination of photo-induced electron-hole pairs and also can provide a large surface area for Cr(VI) removal, both of which are beneficial to the reducing capacity of the nanocomposites. The higher removal efficiency of N-CuMe₂Pc/rGO compared with that of CuPc/rGO is attributed to the higher specific surface area, higher light harvesting, higher conductivity and more negative lowest unoccupied molecular orbital level of N-CuMe₂Pc/rGO. The N-CuMe₂Pc/rGO nanocomposite shows excellent photochemical recyclability which is essential for application in wastewater treatment.

Solid-Phase Microwave Reduction of WO3 by GO for Enhanced Synergistic Photo-Fenton Catalytic Degradation of Bisphenol A

The synergistic photocatalytic Fenton reaction is a powerful advanced oxidation technique for the degradation of persistent organic pollutants. However, microwave-induced thermal effects on the formation of novel structures facilitating the photocatalytic degradation have been rarely reported. Herein, a two-step microwave thermal strategy was developed to synthesize a new hybrid catalyst comprising defective WO_3-x nanowires coupled with reduced graphene oxides (rGOs). Conventionally, microwave methods could induce superhot spots on the GO surface, resulting in the site-specific crystallization and oriented growth of WO₃. However, in the solid phase, localized microwave thermal effects could reduce the interfacial area between WO₃ and rGO and enhance the bonding between them. As for the unique structure and surface properties, the synthesized catalyst enhanced the light absorption, promoted the interfacial charge separation, and increased the carrier density in the photocatalytic processes. In addition, surface formation of W⁴⁺ provided a new pathway for Fe³⁺/Fe²⁺ cycling which linked the photocatalytic reaction and the Fenton process. The optimized catalyst exhibited a remarkable performance in the degradation of bisphenol A with a ∼83% removal yield via a photo-Fenton route. These microwave-induced functionalities of materials for synergistic reactions could also give a new avenue to other photoelectrocatalytic fields and solar cells.

Silver-loaded In2S3-CdIn2S4@X(X=Ag, Ag3PO4, AgI) ternary heterostructure nanotubes treated by electron beam irradiation with enhanced photocatalytic activity

Ternary heterostructure nanotubes of In₂S₃-CdIn₂S₄@X(X = Ag, Ag₃PO₄, AgI) were synthesized with enhanced photocatalytic activity for efficiently degrading pollutants. Electron beam irradiation was employed to artificially introduce interface defects to the heterostructure nanotubes. The experimental results for degrading carmine and Cr⁶⁺ under visible light irradiation showed that the photocatalytic efficiency of In₂S₃-CdIn₂S₄ was improved to some extent by the introduction of silver compounds. DRS results confirmed that the band gaps of In₂S₃-CdIn₂S₄ were reduced to 1.62 eV and 1.58 eV by introducing Ag₃PO₄ and AgI, respectively. Interestingly, the band gap of In₂S₃-CdIn₂S₄@AgI after electron beam irradiation was further reduced to 1.56 eV, resulting in that the degradation time of both Cr⁶⁺ and carmine by In₂S₃-CdIn₂S₄@AgI after high-energy electron beam irradiation was shortened to only 5 min. The XRD spectra of the photocatalysts after five cycles could maintain the original crystal form to a large extent. The OH stretching vibration peaks of In₂S₃-CdIn₂S₄@AgI after electron beam irradiation at 3387 cm^-1 became wider and sharper, thus indicating that the number of free hydroxyl groups on the heterostructure surface significantly increased. PL results showed that electron beam irradiation could significantly reduce the PL emission peak and enhance the utilization of photogenerated charge carriers. EIS results further confirmed that In₂S₃-CdIn₂S₄@AgI processed by electron beam irradiation had higher photogenerated electron-hole separation efficiency. Based on the experimental results, a feasible reaction pathway and photocatalytic mechanism for the degradation of carmine was investigated. ESR results showed that the main active groups in the whole photocatalytic system were •O₂^- and h⁺.

Effect of reduced graphene oxide doping on photocatalytic reduction of Cr(VI) and photocatalytic oxidation of tetracycline by ZnAlTi layered double oxides under visible light

The existence of Cr(VI) and antibiotics in the environment can form the joint contaminant which can be hazardous to the ecosystem. To deal with this, we have explored a plausible method to remove the Cr(VI) and tetracycline (TC) from water by visible light photocatalysis. In this study, a series of reduced graphene oxide@ZnAlTi layered double oxides (rGO@LDO) composites with different doping ratio of rGO were successfully synthesized, which were applied in photocatalytic reduction of Cr(VI) and oxidation of TC. Graphene acts as an electron donor and it can enhance the adsorption of Cr(VI) and TC on the surface of the composites. It's found that the obtained ZnAlTi-LDO composites doped with rGO have higher photo-responsiveness in the visible region. The best-performing rGO@LDO composite (i.e., CGL3) exhibited enhanced visible light-driven photocatalytic Cr(VI) reduction, which was about five times higher than those of ZnAlTi-LDO (without adding hole catcher). The rGO@LDO also showed a satisfactory performance for photocatalytic oxidation of TC with the total organic carbon removal of 80%. However, the doping of rGO did not significantly enhance the removal of TC. The experiment of pH effects demonstrated that acidic pH was favorable to photocatalytic reduction of Cr(VI), while neutral pH was favorable to photocatalytic oxidation of TC. The band structure of ZnAlTi-LDO was first identified, and the E_VB and E_CB of ZnAlTi-LDO are -2.32 and 0.72 V (vs. RHE). This research provides a feasible method to remove Cr(VI) and tetracycline from water by employing ZnAlTi-LDO doped with rGO as photocatalyst.

The Roles of Nanomaterials in Conventional and Emerging Technologies for Heavy Metal Removal: A State-of-the-Art Review

Heavy metal (HM) pollution in waterways is a serious threat towards global water security, as high dosages of HM poisoning can significantly harm all living organisms. Researchers have developed promising methods to isolate, separate, or reduce these HMs from water bodies to overcome this. This includes techniques, such as adsorption, photocatalysis, and membrane removal. Nanomaterials play an integral role in all of these remediation techniques. Nanomaterials of different shapes have been atomically designed via various synthesis techniques, such as hydrothermal, wet chemical synthesis, and so on to develop unique nanomaterials with exceptional properties, including high surface area and porosity, modified surface charge, increment in active sites, enhanced photocatalytic efficiency, and improved HM removal selectivity. In this work, a comprehensive review on the role that nanomaterials play in removing HM from waterways. The unique characteristics of the nanomaterials, synthesis technique, and removal principles are presented. A detailed visualisation of HM removal performances and the mechanisms behind this improvement is also detailed. Finally, the future directions for the development of nanomaterials are highlighted.

Simultaneous and efficient photocatalytic reduction of Cr(VI) and oxidation of trace sulfamethoxazole under LED light by rGO@Cu2O/BiVO4p-n heterojunction composite

Antibiotics and heavy metals often coexist in polluted environment, and the harm of combined pollution is greater than that of single pollution. In this study, a series of graphene supported p-n heterojunction rGO@Cu₂O/BiVO₄ composites are synthesized with different Cu₂O doping for simultaneous detoxification of Cr(VI) and antibiotics. The obtained photocatalysts (rGO@Cu₂O/BiVO₄) with proper loading amount of Cu₂O shows the a high photocatalytic degradation activity for simultaneously efficient Cr(VI) reduction and sulfamethoxazole (SMZ) oxidation under LED light at neutral pH. The Cr(VI) was completely transformed to Cr(III) rather than simply Cr(VI) adsorbed on the surface of rGO@Cu₂O/BiVO₄. The photocatalytic activity of composites can be attributed to excellent electrical conductivity of rGO and the p-n heterojunction between Cu₂O and BiVO₄, which promotes the spatial separation of photogenerated charges at the heterojunction boundary and inhibits of the photogenerated h⁺ and e^- recombination. It's confirmed that h⁺, O₂^- and OH are the main reactive species for the photocatalytic SMZ oxidation, and the most important reactive species is h⁺. Finally, the tentative degradation pathways of SMZ are proposed based on the liquid chromatography-triple quadrupole mass spectrometry analysis. This work provides an effective approach for the treatment of water that contains SMZ and Cr(VI) under LED light.

Performance of Bi2O3/TiO2 prepared by sol-gel on p-Cresol degradation under solar and visible light

Photocatalytic degradation of p-Cresol was evaluated using the mixed oxide Bi₂O₃/TiO₂ (containing 2 and 20% wt. Bi₂O₃ referred as TB2 and TB20) and was compared with bare TiO₂ under simulated solar radiation. Materials were prepared by the classic sol-gel method. All solids exhibited the anatase phase by X-ray diffraction (XRD) and Raman spectroscopy. The synthesized materials presented lower crystallite size and Eg value, and also higher surface area as Bi₂O₃ amount was increased. Bi content was quantified showing near to 70% of theoretical values in TB2 and TB20. Bi₂O₃ incorporation also was demonstrated by X-ray photoelectron spectroscopy (XPS). Characterization of mixed oxides suggests a homogeneous distribution of Bi₂O₃ on TiO₂ surface. Photocatalytic tests were carried out using a catalyst loading of 1 g L^-1 under simulated solar light and visible light. The incorporation of Bi₂O₃ in TiO₂ improved the photocatalytic properties of the synthesized materials obtaining better results with TB20 than the unmodified TiO₂ under both radiation sources.

The Ternary Heterostructures of BiOBr/Ultrathin g-C₃N₄/Black Phosphorous Quantum Dot Composites for Photodegradation of Tetracycline

Herein, we synthesized BiOBr/ultrathin g-C₃N₄/ternary heterostructures modified with black phosphorous quantum dots using a simple water bath heating and sonication method. The ternary heterostructure was then used for the photocatalytic degradation of tetracycline in visible light, with an efficiency as high as 92% after 3 h of irradiation. Thus, the photodegradation efficiency is greatly improved compared to that of ultrathin g-C₃N₄, BiOBr, and black phosphorous quantum dots alone. The synthesized ternary heterostructure improves the charge separation efficiency, thus increasing the photodegradation efficiency. This work provides a new and efficient method for the degradation of antibiotics in the environment.