Green approach for photocatalytic Cu(II)-EDTA degradation over TiO2: toward environmental sustainability

Simultaneous Cu(II)-EDTA decomplexation and Cu(II) recovery using integrated contact-electro-catalysis and capacitive deionization from electroplating wastewater

The complex of heavy metals and organic acids leads to high difficulty in heavy metals separation by traditional technologies. Meanwhile, alkaline precipitation commonly used in industry causes the great consumption of resources and extra pollution. Herein, the effective decomplexation of Cu(Ⅱ)-EDTA and synchronous recycling of Cu2+ were realized by contact-electro-catalysis (CEC) coupled with capacitive deionization (CDI) innovatively. In particular, fluorinated ethylene propylene (FEP) as dielectric powders could generate reactive oxygen species under ultrasonic stimulation, realizing continuous deaminization and decarboxylation of Cu(Ⅱ)-EDTA and accelerating the totally breakage of Cu-O and Cu-N bonds. Additionally, the degradation pathway and intermediates evolution of Cu(Ⅱ)-EDTA were investigated using various characterization methods. It was confirmed that decarboxylation predominantly governed the degradation process of Cu(Ⅱ)-EDTA in CEC. During the course of treatment, the degradation ratio of Cu(Ⅱ)-EDTA reached 86.4 % within 150 min. Impressively, this strategy had satisfactory applicability to other metal combinations and excellent cycle stability. Subsequently, the released Cu ions were captured by CuSe cathode electrode through CDI. This research elucidated the degradation mechanism of persistent organic pollutant during CEC, and provided a novel approach for efficiently treating industrial wastewater containing metal complexes and advancing the exploitation and utilization of new technologies for metal recovery.

Self-catalytic decomplexation of Cu-TEPA and simultaneous recovery of Cu by an electrochemical ozone production system using heterojunction Ni-Sb-SnO2 anode

Heavy metal complexes from the industrial wastewater induce risks for the humans and ecosystems, yet are valuable metal resources. For energy saving and emission reduction goals, the simultaneous decomplexation and recovery of metal resources is the ideal disposal of wastewater with heavy metal complexes. Herein, a self-catalytic decomplexation scheme is developed via an electrochemical ozone production (EOP) system to achieve efficient decomplexation and Cu recovery. The EOP system could achieve 94.36% decomplexation of Cu-TEPA, which is a typical complex in catalyst industrial wastewater, and 86.52% recovery of Cu within 60 min at a current density of 10 mA/cm2. The O3 and •OH generated at the anode would first attack Cu-TEPA to produce Cu-organic nitrogen intermediates, which further catalyze O3 to generate •OH, thus self-enhancing the decomposition process in the EOP system. The released Cu2+ was gradually reduced to Cu+ and finally deposited as Cu2O and Cu to the stainless steel cathode. The technological feasibility was confirmed with other Cu-complexes such as Cu-EDTA and Cu-citrate, and the actual Cu-TEPA-containing industrial wastewater. The results provide new insights regarding the application of EOP in the simultaneous treatment of heavy metal complex wastewater and resource recovery.

Sulfide-modified nanozerovalent iron for rapid decontamination of Cu(Ⅱ) complexes in high-salinity wastewater

Heavy metal complexes receive less attention, but they are more difficult to remove than the free heavy metals. Moreover, the high-salinity wastewaters from various industries hinder the removal of heavy metal complexes. Removal of the metal complexes is a top priority but a challenging task. Herein, a new strategy for removing Cu-EDTA from high-salinity wastewater with sulfide-modified nanozerovalent iron (S-NZVI) was proposed. The S-NZVI exhibited a considerable adsorption capacity for Cu-EDTA (∼83 mg Cu/g) at a high salt concentration (25 g/L NaCl). Similarly, the S-NZVI maintained excellent adsorption performance (∼83 mg Cu/g) in the presence of CaCl2, MgCl2, Na2SO4, and NaNO3 (25 g/L). The S-NZVI showed extremely high efficiency for Cu-EDTA removal; 50 mg/L of Cu-EDTA was almost completely removed in 1 min, and the kobs was approximately 1.5 g/(mg min). The S-NZVI showed an extensive pH working range, and within the pH range of 2-9, the Cu-EDTA was removed completely within 5 min. The excellent removal performance of the S-NZVI was due to the high reactivity and high affinity of NZVI for Cu, as well as the special substitution of Fe2+ and the interfacial reactions between S-NZVI and the copper complexes. Compared with other studies of Cu complex removal, removal with S-NZVI was a simpler process with higher efficiency. In brief, S-NZVI efficiently removed Cu complexes from harsh water environments and was reused many times. The process was simple and efficient and has broad application prospects.

Highly Selective Electrocatalytic CuEDTA Reduction by MoS2 Nanosheets for Efficient Pollutant Removal and Simultaneous Electric Power Output

Electrocatalytic reduction of ethylenediamine tetraacetic acid copper (CuEDTA), a typical refractory heavy metal complexation pollutant, is an environmental benign method that operates at mild condition. Unfortunately, the selective reduction of CuEDTA is still a big challenge in cathodic process. In this work, we report a MoS2 nanosheet/graphite felt (GF) cathode, which achieves an average Faraday efficiency of 29.6% and specific removal rate (SRR) of 0.042 mol/cm2/h for CuEDTA at - 0.65 V vs SCE (saturated calomel electrode), both of which are much higher than those of the commonly reported electrooxidation technology-based removal systems. Moreover, a proof-of-concept CuEDTA/Zn battery with Zn anode and MoS2/GF cathode is demonstrated, which has bifunctions of simultaneous CuEDTA removal and energy output. This is one of the pioneer studies on the electrocatalytic reduction of heavy metal complex and CuEDTA/Zn battery, which brings new insights in developing efficient electrocatalytic reduction system for pollution control and energy output.

Novel strategy for copper precipitation from cupric complexes wastewater: Catalytic oxidation or reduction self-decomplexation?

Cupric (Cu(II)) complexes in industrial wastewater are responsible for the failure of conventional alkaline precipitation, but the properties of cuprous (Cu(I)) complexes at alkaline circumstance have not been focused. This report proposed a novel strategy for the remediation of Cu(II)-complexed wastewater by coupling alkaline precipitation with green benign reductant, namely, hydroxylamine hydrochloride (HA). This remediation process (HA-OH) exhibits superior Cu removal efficiency that cannot be achieved with the same dosage of oxidants (3 mM). The possibility of Cu(I) activated O₂ catalysis and self-decomplexation precipitation were investigated, and the results identified that ¹O₂ was generated from Cu(II)/Cu(I) cycle, but it was insufficient to annihilate organic ligands. Cu(I) self-decomplexation was the dominate mechanism of Cu removal. For real industrial wastewater, HA-OH process can realize the efficient Cu₂O precipitation and Cu recovery. This novel strategy utilized intrinsic pollutant in wastewater without introducing other metals, complicated materials, and expensive equipment, broadening the insight for the remediation of Cu(II)-complexed wastewater.

Coagulation characteristic and mechanism of Fe(III) salts toward typical Cr(III) complexes in wastewater treatment

Cr(III) complexes are typical pollutants in various industrial wastewater and pose a serious threat to the ecosystem and humans. The coagulation process is commonly used in water treatment plants, yet its removal characteristic and mechanism toward Cr(III) complexes have been rarely reported. In this study, the Fe(III) coagulation process was adopted for the evaluation of Cr(III) complex removal in terms of Cr residual concentration as well as floc size. The results showed that Fe(III) with a dose of 0.8 mM removed more than 80% of total Cr for Cr³⁺ and Cr(III)-acetate, whereas poor removal rate (~ 50%) was obtained for Cr(III)-citrate under the same conditions. Neutral and alkaline conditions facilitated Cr(III)-acetate removal by Fe(III) coagulation, while limited influence was observed for Cr(III)-citrate with various pH. The main removal mechanism of Cr(III)-acetate was precipitation. Cr(III)-citrate elimination largely relied on the adsorption property and sweeping effect of Fe floc. Moreover, Cr(III)-acetate was easier to be separated from a solution since the generated floc sizes were 270 μm. Flocs that formed in the Cr(III)-citrate treatment were only 0.3 μm, resulting in separation difficulties during the coagulation process. The presence of Cr(III)-acetate and Cr(III)-citrate caused a significant decline in membrane flux. This study provided fundamental knowledge of Fe coagulation treatment in Cr(III) complex-containing wastewater.

Sustainable decontamination of heavy metal in wastewater and soil with novel rectangular wave asymmetrical alternative current electrochemistry

A new concept of removal and recovery of heavy metals and simultaneous regeneration and reuse of ethylenediamine-tetraacetic acid (EDTA) in soil washing effluent containing metal-EDTA complexes is proposed, which is used to remediate heavy metal contaminated soil. To achieve this goal, soil washing approach coupled with rectangular wave asymmetrical alternative current electrochemistry (RW-ACE) equipped with amidoxime-functionalized electrodes (Ami-CF) is employed. With high hydrophilicity and strong binding affinity, Ami-CF could specifically compete for heavy metals over EDTA under electric field. RW-ACE system is found successfully to achieve the non-destructive decomplexation of heavy metal-EDTA, and then regenerate EDTA for highly recycling, which saves as high as 98.9 % EDTA consumption compared with conventional washing method. Moreover, more than 90% of heavy metals are recovered and deposited on the electrode with a majority of them existed as zero-valence state as evidenced by XPS. The RW-ACE method is universal for various heavy metals such as Cu²⁺, Zn²⁺, Cd²⁺, and Pb²⁺ in an authentic contaminated soil, and the loss of soil nutrient is very limited. Along with long-term assessment and operation cost estimation, the RW-ACE method is a sustainable remediation approach for the heavy metal polluted wastewater and soils, and easily scaled up for field practice.

Aquatic photochemistry of Cu(II) in the presence of As(III): Mechanistic insights from Cu(III) production and As(III) oxidation under neutral pH conditions

Surface complexation between arsenite (As(III)) and colloidal metal hydroxides plays an important role not only in the immobilization and oxidation of As(III) but also in the cycle of the metal and the fate of their ligands. However, the photochemical processes between Cu(II) and As(III) are not sufficiently understood. In this work, the photooxidation of As(III) in the presence of Cu(II) under neutral pH conditions was investigated in water containing 200 μM Cu(II) and 5 μM As(III) under simulated solar irradiation consisting of UVB light. The results confirmed the complexation between As(III) and Cu(II) hydroxides, and the photooxidation of As(III) is attributed to the ligand-to-metal charge transfer (LMCT) process and Cu(III) oxidation. The light-induced LMCT process results in simultaneous As(III) oxidation and Cu(II) reduction, then produced Cu(I) undergoes autooxidation with O₂ to produce O₂^•⁻ and H₂O₂, and further the Cu(I)-Fenton reaction produces Cu(III) that can oxidize As(III) efficiently (k_{Cu(III)+As(III)} = 1.02 × 10⁹ M^-1 s^-1). The contributions from each pathway (ρ_{rCu(II)-As(III)+hv} = 0.62, ρ_{rCu(III)+As(III)} = 0.38) were obtained using kinetic analysis and simulation. Sunlight experiments showed that the pH range of As(III) oxidation could be extended to weak acidic conditions in downstream water from acid mine drainage (AMD). This work helps to understand the environmental chemistry of Cu(II) and As(III) regarding their interaction and photo-induced redox reactions.

Simultaneous capturing of mixed contaminants from wastewater using novel one-pot chitosan functionalized with EDTA and graphene oxide adsorbent

The emergence of inorganic and organic contaminants has raised great concerns owing to their adverse impact on human health and ecological security. Herein, first time one-pot process was applied for chitosan (CS) functionalization using graphene oxide (GO) and ethylenediaminetetraacetic acid (EDTA) for simultaneous capturing of toxic inorganic (lead (Pb²⁺) and cadmium (Cd²⁺)) and organic (ciprofloxacin (CIP) and sildenafil (SDF)) contaminants from wastewater. In this approach, we believe that CS would work as a backbone, GO would capture both inorganic and organic contaminants via electrostatic interactions, while EDTA would make complexation with heavy metals. Various parameters including pH, reaction time, concentration, reusability etc. were evaluated to achieve the best experimental result in monocomponent system. The prepared adsorbent displayed an excellent monolayer adsorption capacity of 351.20 and 264.10 mg g^-1 for Pb²⁺ and Cd²⁺, respectively, while a heterogeneous sorption capacity of 75.40 and 40.90 mg g^-1 for CIP and SDF, respectively. The kinetics data fitted well to Pseudo-second order (PSO) kinetics model for both types of contaminants and gave faster interaction towards metal ions (higher k₂) than organic contaminants. Experimental results showed excellent adsorption efficiencies at environmental levels in the capturing of both inorganic and organic contaminants at the same time from polluted water. The capturing mechanism of both types of contaminants was explained by elemental mapping, EDS, and FT-IR spectra. Overall, easy synthesis, excellent capturing capacity, and reusability imply that the prepared adsorbent has a sufficient potential for the treatment of co-existing toxic contaminants in water.

Sequestration of free and chelated Ni(II) by structural Fe(II): Performance and mechanisms

Ni(II) and chelated Ni(II) in wastewater are of environmental concern. This study explores the sequestration potential of structural Fe(II) in solid phase (≡Fe(II)) on Ni(II) and EDTA-Ni(II) using freshly prepared ferrous hydroxyl complex (FHC) as the Fe(II)-bearing mineral. The 1 mM Ni(II) could be completely sequestrated in 20 min by 3 mM FHC, although the sequestrated Ni(II) was partially released after 20 min. It is calculated that up to 156 mg Ni(II)/g Fe(II) can be sequestrated by ≡Fe(II) under neutral pH and anaerobic condition. According to the characterizations of the solid products, the large surface area for Ni(II) adsorption and the high ≡Fe(II) reduction capacity for Ni(II) reduction are the main contributors to the Ni(II) sequestration. After the reaction, the FHC is transformed to stable Fe-Ni layered double hydroxides. The concomitant ions can be either promotional or inhibitory to the sequestration performance depending on the ion type. The combination of FHC and Fe(III) can effectively sequestrate EDTA-Ni(II), whereas FHC alone has a low efficiency. Fe(III) substitutes Ni(II) from the EDTA-Ni(II), benefiting the subsequent Ni(II) sequestration by ≡Fe(II). This study demonstrates that ≡Fe(II) suspension is an cost-effective option for remediating Ni(II)-containing wastewater.

Treatment of Ni-EDTA containing wastewater by electrochemical degradation using Ti3+ self-doped TiO2 nanotube arrays anode

Ethylene diamine tetraacetic acid (EDTA) could form stable complexes with nickel due to its strong chelation. Ni-EDTA has significant impacts on human health because of its acute toxicity and low biodegradability, thus some appropriate approaches are required for its removal. In this research, a Ti³⁺ self-doped TiO₂ nanotube arrays electrode (ECR-TiO₂ NTA) was prepared and employed in electrochemical degradation of Ni-EDTA. The oxygen evolution potential of ECR-TiO₂ NTA was 2.6 V vs. SCE. More than 96% Ni-EDTA and 88% TOC was removed after reaction for 120 min at current density 2 mA cm^-2 at pH 4.34. The degradation of Ni-EDTA was mainly through the cleavage of amine group within Ni-EDTA and furthermore decomposed it into small molecular acids and inorganic ions including NH₄⁺and NO₃^-. The electro-deposition of nickel ions at cathode was confirmed by XPS and was greatly affected by the pH of solution. The effects of current density, initial Ni-EDTA concentration, initial pH of solution and HCO₃^- concentration on Ni-EDTA degradation were investigated. The results exhibited that the ECR-TiO₂ NTA had excellent efficiencies in electrochemical degradation of Ni-EDTA. The LSV analysis suggested that Ni-EDTA oxidation on ECR-TiO₂ NTA anode and the production of hydroxyl radical (·OH) on the anode played an important role in the removal of Ni-EDTA.

Developing the amazing photocatalyst of ZnAg2GeSe4, ZnAg2Ge0.93Fe0.07Se4 and ZnAg2Ge0.86Fe0.14Se4 through the computational explorations by four DFT functionals

For developing the stannite type quarterly crystal photocatalyst, the electronic structure and optical properties of ZnAg₂GeSe₄, ZnAg₂Ge_0.93Fe_0.07Se₄ and ZnAg₂Ge_0.86Fe_0.14Se₄ were calculated and compared with the parent stannite type quarterly crystal, ZnAg₂GeS₄. First of all, the four functionals, such as GGA with PBE, GGA with RPBE, GGA with WC and LDA with CA-PZ functionals were used for primary screening of electronic band structure and structural geometry for ZnAg₂GeS₄ while the band gap was in 0.93, 0.97, 0.77 and 0.67 eV, respectively. It must be mentioned that the experimental value of ZnAg₂GeS₄ was 0.94 eV so that the GGA with PBE showed the overlapping value of band gap. The main focus of this paper is to evaluate the band structure of newly predicted the stannite type quarterly crystal, ZnAg₂GeSe₄ using four methods replacing the Sulfur atom by Serium atom on ZnAg₂GeS₄. The band gap for four methods, such as GGA with PBE, GGA with RPBE, GGA with WC and LDA with CA-PZ functionals, were calculated in 0.84 eV, 0.92 eV, 0.68 eV and 0.58 eV. Afterward, Fe atom was doped by two portions, like 7% and 14%, to make the empirical formula, ZnAg₂Ge_0.93Fe_0.07Se₄ and ZnAg₂Ge_0.86Fe_0.14Se₄. The numerical values of band gaps for ZnAg₂Ge_0.93Fe_0.07Se₄ and ZnAg₂Ge_0.86Fe_0.14Se₄ were 0.43 eV, 0.53 eV, 0.35 eV and 0.18 eV and 0.24 eV, 0.31 eV, 0.18 eV and 0.08 eV, respectively, using the four respected DFT methods. For their contributed orbitals of each atom on crystal, the density of state and the partial density of state for ZnAg₂GeSe₄, ZnAg₂Ge_0.93Fe_0.07Se₄ and ZnAg₂Ge_0.86Fe_0.14Se₄ crystals were simulated through the GGA with PBE method as standard regarding the calculation of band gap study comparison with experimental magnitude. For giving the further information about the nature in case of optical evidence, the six optical properties, such as absorption, reflection, refractive index, conductivity, dielectric function and loss function were calculated, and make a comparative study. In case of UV light absorption in lighten to optical parameters, the ZnAg₂Ge_0.86Fe_0.14Se₄ can show the highest absorption up to convenience energy region as photocatalyst.

Self-Enhanced Decomplexation of Cu-Organic Complexes and Cu Recovery from Wastewaters Using an Electrochemical Membrane Filtration System

Heavy metals in industrial wastewaters are typically present as stable metal-organic complexes with their cost-effective treatment remaining a significant challenge. Herein, a self-enhanced decomplexation scenario is developed using an electrochemical membrane filtration (EMF) system for efficient decomplexation and Cu recovery. Using Cu-EDTA as a model pollutant, the EMF system achieved 81.5% decomplexation of the Cu-EDTA complex and 72.4% recovery of Cu at a cell voltage of 3 V. The ^•OH produced at the anode first attacked Cu-EDTA to produce intermediate Cu-organic complexes that reacted catalytically with the H₂O₂ generated from the reduction of dissolved oxygen at the cathode to initiate chainlike self-enhanced decomplexation in the EMF system. The decomplexed Cu products were further reduced or precipitated at the cathodic membrane surface thereby achieving efficient Cu recovery. By scavenging H₂O₂ (excluding self-enhanced decomplexation), the rate of decomplexation decreased from 8.8 × 10^-1 to 4.1 × 10^-1 h^-1, confirming the important role of self-enhanced decomplexation in this system. The energy efficiency of this system is 93.5 g kWh^-1 for Cu-EDTA decomplexation and 15.0 g kWh^-1 for Cu recovery, which is much higher than that reported in the previous literature (i.e., 7.5 g kWh^-1 for decomplexation and 1.2 g kWh^-1 for recovery). Our results highlight the potential of using EMF for the cost-effective treatment of industrial wastewaters containing heavy metals.

Cu(II)-EDTA removal by a two-step Fe(0) electrocoagulation in near natural water: Sequent transformation and oxidation of EDTA complexes

The widely usage of ethylenediaminetetraacetic acid (EDTA) arises environmental concerns on toxic metal mobilization, and challenges the conventional processes in water treatment. In the study Cu(II)-EDTA in near natural water was efficiently removed during a two-step electrocoagulation using Fe(0) anode (Fe-EC), including a transformation to Fe(III)-EDTA induced mainly by structural Fe(II) in anoxic Fe-EC and further degradation in oxic Fe-EC. The degradation of Fe(III)-EDTA was mostly attributed to an oxygen activation mechanism that involving O₂^- and hydroxyl radical (OH) generation, as validated by the quenching experiments and electron spin resonance. Furthermore, O₂^- generated during Fe(II) oxidation took a dominant role on Fe(III)/Fe(II)-EDTA transformation instead of electrochemical reduction. Six intermediates during the Fe(III)-EDTA degradation were identified by LC-Q-TOF, indicating a pathway of stepwise breakage of NC bonds. The results revealed in this work is helpful to understand the contribution and fate of EDTA during Fe-EC treatment of metal-EDTA polluted water.

Removal of lead complexes by ferrous phosphate and iron phosphate: Unexpected favorable role of ferrous ions

The high chemical stability of lead complexes in solution precludes most traditional removal methods. Achieving the efficient, cost-effective, and environmentally friendly removal of metal complexes from wastewater is a challenge. In this study, ferrous phosphate and iron phosphate were used to treat wastewater containing EDTA-Pb, and the differences in their removal processes were compared. Both materials enabled efficient removal of the EDTA-Pb complex from 50 mg Pb/L to <1 mg Pb/L, and the leaching of Fe was <50 mg/L. More attractively, the maximum adsorption capacity of ferrous phosphate significantly increased from 80.44 mg Pb/g to 436.68 mg Pb/g as the reaction environment changed from aerobic to anoxic. The concentration of Pb was reduced to the sub-ppm level by ferrous phosphate even when the initial concentration of EDTA-Pb was 300 mg/L. In-depth exploration of the removal mechanism of EDTA-Pb demonstrated that the synergistic effect of Fe²⁺ and Fe³⁺ contributed to the high removal efficiency of EDTA-Pb by ferrous phosphate. Moreover, ferrous phosphate was minimally affected by salinity and organics, but the iron phosphate performance was significantly suppressed. The potential application of ferrous phosphate was further explored by processing explosive wastewater containing lead complexes. The results showed that the residual Pb content was 0.94 mg/L (lower than the discharge standard of China) and the removal performance of iron phosphate was suppressed. The results demonstrate that ferrous phosphate is a promising material for the decontamination of EDTA-Pb-contaminated water.

Efficient removal of Cu(II) organic complexes by polymer-supported, nanosized, and hydrated Fe(III) oxides through a Fenton-like process

In this study, a polymer-supported, nanosized, and hydrated Fe(III) oxide (HFOD) was developed as a Fenton-like catalyst for the efficient removal of metal complexes in water. HFOD was prepared through the irreversible impregnation of hydrated iron(III) oxide (HFO) nanoparticles into cation exchange resin and characterized through X-ray photoelectron spectroscopy (XPS) and ion chromatography. The mechanism of Cu(II) ion removal and the degradation pathway of Cu(II)-citrate were analyzed through UV-vis spectrophotometry (UV) and liquid chromatography-mass spectrometry (LC-MS). The optimal removal rate of Cu(II) and TOC by a Fenton-like reaction at pH 4 and 40 mM H₂O₂ reached 81.6 % and 75.6 %, respectively. The removal efficiency of Cu(II)-citrate was remarkably affected with the addition of humic acid. However, the addition of competitive ions did not significantly reduce the removal rate of Cu(II)-citrate, thereby proving that the Fenton-like reaction by HFOD had a certain salt tolerance. Simultaneously, hydroxyl radical (•OH) was verified as the main free radical for Cu(II)-citrate degradation in a Fenton-like reaction, and citrate degradation was a process decarboxylation. HFOD recycling experiments and stability experiments showed that HFOD had high stability with good acid/alkali resistance and showed remarkable potential in the practical application of fixed-bed as catalysts for Fenton-like reactions.

Sludge reduction and cost saving in removal of Cu(II)-EDTA from electroplating wastewater by introducing a low dose of acetylacetone into the Fe(III)/UV/NaOH process

Cu(II)-EDTA is highly stable in a wide pH range (3.0∼12.0) and hard to be removed by the conventional precipitation method. Fe(III) displacement/UV photolysis/alkaline precipitation [Fe(III)/UV/NaOH] has been proposed as a promising method for the removal of Cu(II)-EDTA. Nevertheless, a high dose of Fe(III) is needed in this combined process, resulting in the production of a large amount of hazardous sludge. The photochemistry of Fe(III) is known to be ligand-dependent. Fe(III)-oxalate complexes are strongly photoactive. However, the addition of oxalic acid to the Fe(III)/UV/NaOH process was of little help. Acetylacetone (AA) is a good chelating ligand for many metals and has been proved as an efficient photo-activator. By introducing a low dose of AA ([AA]/[Cu] = 1.5) into the Fe(III)/UV/NaOH process, the Fe(III) dosage ([Fe]/[Cu]) was reduced from 10.4 to 3.2. As a result, the chemical cost was reduced from 13.9 to 7.6 kW h/m³. Meanwhile, the energy cost in the UV photolysis was reduced from 1066.5 to 752.4 kW h/m³. Most importantly, the sludge yields were reduced from 8.3 to 2.7 kg/m³ in a simulated wastewater and from 101.8 to 30.8 kg/m³ in a real electroplating wastewater. Such a sludge reduction is of great significance in mitigating the load of landfill.

Non-thermal plasma oxidation of Cu(II)-EDTA and simultaneous Cu(II) elimination by chemical precipitation

Cu²⁺ readily complexes with ethylenediaminetetraacetic acid (EDTA) to form a heavy metal complex (Cu-EDTA) that is typical in the effluents from mining and electroplating industries. It was difficult for the classical alkaline precipitation method to eliminate the heavy metal complex due to the strong bonding ability between Cu(II) and EDTA. Cu(II) release and removal performance after Cu-EDTA decomplexation in a non-thermal plasma oxidation system was carried out in this study. The removal process was characterized by chemical oxygen demand, total organic carbon, atomic force microscopy, and electroconductivity analysis. The toxicity effect of the treated Cu-EDTA solution was also tested by photobacterium bioassay. The experimental results showed that 80.2% of Cu was released and removed within 60 min of the non-thermal plasma treatment/alkaline precipitation. Relatively higher energy input, lower Cu-EDTA concentration, and acidic conditions were necessary to obtain greater Cu release and removal performance, and there existed an appropriate air flow rate for high-efficient Cu release and removal. O₂^-, OH, ¹O₂, and O₃ were the main active substances leading to Cu²⁺ release. Its residual toxicity to P.phosphoreum sp.-T3 was significantly reduced after treatment.

Removal of chelated heavy metals from aqueous solution: A review of current methods and mechanisms

Water contamination with heavy metal ions and organic compounds such as citrate, ethylenediaminetetraacetic acid, tartrate, pharmaceuticals, surfactants and natural organic matter, is a serious problem in the natural environment. Although many methods have been effectively applied to the removal of heavy metal complexes from aqueous solution, there is a lack of information available on the mechanisms, advantages and disadvantages of these various methods. This review summarizes the various treatment methods applied to the removal of heavy metal complexes, with a summary of the mechanisms of action and recent research progress. The methods reviewed in detail include electrolysis, membrane separation, adsorption, precipitation, replacement-coprecipitation, TiO₂ photocatalysis and Fenton oxidation-precipitation, with the advantages and disadvantages of each method discussed. Furthermore, the heavy metal complex removal mechanisms are analyzed comprehensively. Results show that the adsorption method exhibited unique merits, showing much promise for future development. Finally, this review comprehensively analyzes future prospects and developments in methods for removal of chelated heavy metals.

Decomposition of complexed Pb(II) and subsequent adsorption of Pb(II) with yolk-shell Fe3O4@ hydrous zirconium oxide sphere

Purification of water containing heavy metals that are complexed by organic chelating agents remains a challenging task. In this study, a yolk-shell Fe₃O₄@hydrous zirconium oxide (Zr(OH)_x) sphere sphere (YHZOs) nanomaterial was evaluated for its ability to remove ethylene diamine tetraacetic acid complexed Pb²⁺ (Pb-EDTA) from aqueous solution. Specifically, it is hypothesized that upon addition of H₂O₂, the Fe₃O₄ core of YHZOs served as a Fenton-type catalyst that results in oxidation of the Pb-complexed EDTA, and the Zr(OH)_x shell acted as an adsorbent, removing the released Pb²⁺ from solution. From an aqueous solution containing 0.1 mM Pb-EDTA at pH 5, 0.5 g/L YHZOs, and 20 mM H₂O_2, TOC reduction and Pb removal were determined to be 65.3% and 89.8%, respectively. HPLC-MS, IC and continuous flow analyzer results identified major intermediates of EDTA decay to be ethylenediaminetriacetate, (ED3A), ethylenediamine-N,N'-diacetate (ED2A), nitrilotriacetate (NTA), iminodiacetate (IDA), ethylenediamine (EDA), acetic acid, formic acid, oxalic acid, ammonia, and nitrate, with the first 5 species having some affinity to remain complexed to Pb²⁺. The adsorption of Pb²⁺ onto the Zr(OH)_x shells was confirmed by scanning transmission electron microscopy (STEM) with mapping and X-ray photoelectron spectra (XPS). Moreover, the Pb²⁺-adsorbed YHZOs could be easily recovered due to their magnetic properties, with the Pb²⁺ rinsed from them at low pH. Indeed, reused for five cycles showed only minor capacity loss. These findings suggest that the removal of chelated Pb²⁺ from water, and presumably other heavy metals, by yolk-shell Fe₃O₄@Zr(OH)_x may prove to be a useful technology for some contaminated waters.

Autocatalytic Decomplexation of Cu(II)-EDTA and Simultaneous Removal of Aqueous Cu(II) by UV/Chlorine

Traditional processes usually cannot enable efficient water decontamination from toxic heavy metals complexed with organic ligands. Herein, we first reported the removal of Cu(II)-EDTA by a UV/chlorine process, where the Cu(II)-EDTA degradation obeyed autocatalytic two-stage kinetics, and Cu(II) was simultaneously removed as CuO precipitate. The scavenging experiments and EPR analysis indicated that Cl^• accounted for the Cu(II)-EDTA degradation at diffusion-controlled rate (∼10¹⁰ M^-1 s^-1). Mechanism study with mass spectrometry evidence of 11 key intermediates revealed that the Cu(II)-EDTA degradation by UV/chlorine was an autocatalytic successive decarboxylation process mediated by the Cu(II)/Cu(I) redox cycle. Under UV irradiation, Cu(I) was generated during the photolysis of the Cl^•-attacked complexed Cu(II) via ligand-to-metal charge transfer (LMCT). Both free and organic ligand-complexed Cu(I) could form binary/ternary complexes with ClO^-, which were oxidized back to Cu(II) via metal-to-ligand charge transfer (MLCT) with simultaneous production of Cl^•, resulting in the autocatalytic effect on Cu(II)-EDTA removal. Effects of chlorine dosage and pH were examined, and the technological practicability was validated with authentic electroplating wastewater and other Cu(II)-organic complexes. This study shed light on a new mechanism of decomplexation by Cl^• and broadened the applicability of the promising UV/chlorine process in water treatment.

Fabrication of a full-spectrum-response Cu2(OH)2CO3/g-C3N4 heterojunction catalyst with outstanding photocatalytic H2O2 production performance via a self-sacrificial method

Over the past few decades, near infrared light (NIR), as an important part of sunlight, has seldom been utilized in photocatalytic reactions.

Enhanced photoredox water splitting of Sb–N donor–acceptor pairs in TiO2

The development of noble-metal-free TiO₂-based catalysts is of significant interest for photoredox H₂ production.

Novel Cu(II)-EDTA Decomplexation by Discharge Plasma Oxidation and Coupled Cu Removal by Alkaline Precipitation: Underneath Mechanisms

Strong complexation between heavy metals and organic complexing agents makes the heavy metals difficult to be removed by classical chemical precipitation. In this study, a novel decomplexation method was developed using discharge plasma oxidation, which was followed by alkaline precipitation to treat water containing heavy metal-organic complex, that is, Cu-ethylenediaminetetraacetic acid (Cu-EDTA). The decomplexation efficiency of Cu complex reached up to nearly 100% after 60 min's oxidation by discharge plasma, which was accompanied by 82.1% of total organic carbon removal and energy efficiency of 0.62 g kWh^-1. Presence of free Cu²⁺ favored Cu-EDTA decomplexation, whereas the presence of excessive EDTA depressed this process. Cu-EDTA decomplexation was mainly driven by the produced ¹O₂, O₂^•-, O₃, and •OH by discharge plasma. Cu-EDTA decomplexation process was characterized by UV-vis, ATR-FTIR, total organic carbon, and three-dimensional fluorescence diagnosis. The main intermediates including Cu-EDDA, Cu-IDA, Cu-NTA, small organic acids, NH₄⁺, and NO₃^- were identified, accompanied by Cu²⁺ releasing. The followed precipitation process removed 78.1% of Cu²⁺, and Cu-associated precipitates included CuCO₃, Cu₂CO₃(OH)₂, CuO, and Cu(OH)₂. A possible pathway of Cu complex decomplexation and Cu²⁺ removal in such a system was proposed.

Photocatalytic conversion of ethylenediaminetetraacetic acid dissolved in real electroplating wastewater to hydrogen in a solar light-responsive system

A sustainable and multifunctional photocatalysis-based technology has been established herein for simultaneous hydrogen generation and oxidation of ethylenediaminetetraacetic acid (EDTA) in real electroplating wastewater. When the photocatalyst concentration was 4 g/L and electroplating wastewater pH was 6, optimal adsorptions of EDTA^2-, H⁺, and H₂O were observed, while hydrogen generation efficiency reached 305 µmol/(h g). Owing to EDTA oxidation and occupation of the active sites of the photocatalyst by Ni ions or Ni-EDTA chelates, the charge separation and adsorptions of H⁺ and H₂O decreased, reducing hydrogen generation efficiency with time. The lower EDTA and Ni concentrations in treated wastewater showed that photocatalytic conversion of EDTA in real electroplating wastewater to enhance hydrogen generation efficiency can be a practical alternative energy production technology. This study provided a novel idea to enhance the value of electroplating wastewater, to build a hydrogen generation route with no consumption of a valuable resource, and to reduce EDTA and Ni concentrations in electroplating wastewater.

Efficient removal of EDTA-complexed Cu(II) by a combined Fe(III)/UV/alkaline precipitation process: Performance and role of Fe(II)

Efficient removal of heavy metal-EDTA complexes from water remains a challenge because of their good solubility and chemical stability. Herein, we employed a proprietary process, i.e., the Fe(III) displacement/UV irradiation/alkaline precipitation (denoted as Fe(III)/UV/OH), to enable an efficient removal of Cu(II)-EDTA complex from 19.2 mg Cu(II)/L to <1 mg Cu(II)/L. The combined process includes Fe(III) replacement with the complexed Cu(II) to form Fe(III)-EDTA and release the free Cu(II), UV-mediated catalytic decarboxylation of EDTA to form amine ligands and reduction of Fe(III) to Fe(II), and the final removal of Cu(II) through precipitation. The in situ formed Fe(II) is crucial to the final Cu(II) removal because it tends to form stable complexes with amine ligands (EDTA and its decarboxylation products), thereby inhibiting their re-complexation with the released Cu(II) and facilitating the formation of copper precipitates. Consequently, the methods capable of prolonging the life of Fe(II), e.g., increasing the Fe(III) addition or direct addition of Fe(II) into the Cu(II)-EDTA solution and deoxygenating the solution, could dramatically enhance the final Cu(II) removal. We also optimized the operational conditions of the process at the initial Cu(II)-EDTA of 19.2 mg Cu(II)/L.

A Ag synchronously deposited and doped TiO2 hybrid as an ultrasensitive SERS substrate: a multifunctional platform for SERS detection and photocatalytic degradation

We proposed a Ag synchronously deposited and doped TiO₂ hybrid as a dual-function platform for ultrasensitive SERS detection and efficient photocatalytic degradation.

One-pot synthesis of trifunctional chitosan-EDTA-β-cyclodextrin polymer for simultaneous removal of metals and organic micropollutants

The global contamination of water resources with inorganic and organic micropollutants, such as metals and pharmaceuticals, poses a critical threat to the environment and human health. Herein, we report on a bio-derived chitosan-EDTA-β-cyclodextrin (CS-ED-CD) trifunctional adsorbent fabricated via a facile and green one-pot synthesis method using EDTA as a cross-linker, for the adsorption of toxic metals and organic micropollutants from wastewater. In this system, chitosan chain is considered as the backbone, and the immobilized cyclodextrin cavities capture the organic compounds via host-guest inclusion complexation, while EDTA-groups complex metals. The thoroughly characterized CS-ED-CD was employed for batch adsorption experiments. The adsorbent displayed a monolayer adsorption capacity of 0.803, 1.258 mmol g-1 for Pb(II) and Cd(II) respectively, while a heterogeneous sorption capacity of 0.177, 0.142, 0.203, 0.149 mmol g-1 for bisphenol-S, ciprofloxacin, procaine, and imipramine, respectively. The adsorption mechanism was verified by FT-IR and elemental mapping. Importantly, the adsorbent perform is effective in the simultaneous removal of metals and organic pollutants at environmentally relevant concentrations. All these findings demonstrate the promise of CS-ED-CD for practical applications in the treatment of micropollutants. This work adds a new insight to design and preparation of efficient trifunctional adsorbents from sustainable materials for water purification.

Real-time monitoring of the degradation of Cu(II)-EDTA in H2O2/UV using illumination-assisted droplet spray ionization mass spectrometry

Illumination-assisted droplet spray ionization (IA-DSI) mass spectrometry was developed for in situ analysis and real-time monitoring of photolysis reactions. In IA-DSI, a photolysis reaction occurs on a corner of a cover slip positioned in front of a mass spectrometer, and the generated reaction intermediates are ionized via the corner and are directed to the inlet and analyzed by a mass spectrometer. IA-DSI is contaminant-free, low-cost and simple, and was demonstrated for in situ analysis and real-time monitoring of the degradation of Cu(II)-EDTA in H₂O₂/UV. The reaction times varied from seconds to minutes, and three new reaction intermediates were detected and identified by tandem mass spectrometry. More importantly, the proposed initiation site of Cu(II)-EDTA at the carboxyl group by ∙OH attack was verified for the first time. The degradation of Cu(II)-EDTA occurred through its chemical bonds broken at the carboxyl group, at the amino group, and between EDTA and Cu(II). By sampling in situ and monitoring in real time, IA-DSI provides advantages in simplifying the analysis process for photolysis reaction intermediates and products, and can detect photolysis reaction intermediates and products in less than a second.

Substrate-Coated Illumination Droplet Spray Ionization: Real-Time Monitoring of Photocatalytic Reactions

Real-time monitoring of photocatalytic reactions facilitates the elucidation of the mechanisms of the reactions. However, suitable tools for real-time monitoring are lacking. Herein, a novel method based on droplet spray ionization named substrate-coated illumination droplet spray ionization (SCI-DSI) for direct analysis of photocatalytic reaction solution is reported. SCI-DSI addresses many of the analytical limitations of electrospray ionization (ESI) for analysis of photocatalytic-reaction intermediates, and has potential for both in situ analysis and real-time monitoring of photocatalytic reactions. In SCI-DSI-mass spectrometry (MS), a photocatalytic reaction occurs by loading sample solutions onto the substrate-coated cover slip and by applying UV light above the modified slip; one corner of this slip adjacent to the inlet of a mass spectrometer is the high-electric-field location for launching a charged-droplet spray. After both testing and optimizing the performance of SCI-DSI, the value of this method for in situ analysis and real-time monitoring of photocatalytic reactions was demonstrated by the removal of cyclophosphamide (CP) in TiO₂/UV. Reaction times ranged from seconds to minutes, and the proposed reaction intermediates were captured and identified by tandem mass spectrometry. Moreover, the free hydroxyl radical (·OH) was identified as the main radicals for CP removal. These results show that SCI-DSI is suitable for in situ analysis and real-time monitoring of CP removal under TiO₂-based photocatalytic reactions. SCI-DSI is also a potential tool for in situ analysis and real-time assessment of the roles of radicals during CP removal under TiO₂-based photocatalytic reactions.Graphical Abstract.

Preparation of Cu(ii) porphyrin–TiO2 composite in one-pot method and research on photocatalytic property

A promising strategy for porphyrin–TiO₂ photocatalyst preparation by using sol–gel process and solvothermal condition showed prospective utilization in the field of dye pollutant photodegradation.

Sequestration of chelated copper by structural Fe(II): Reductive decomplexation and transformation of Cu(II)-EDTA

Chelated coppers, such as Cu(II)-EDTA, are characteristically refractory and difficult to break down because of their high stability and solubility. Cu(II)-EDTA sequestration by structural Fe(II) (Fe(II)) was investigated intensively in this study. Up to 101.21mgCu(II)/gFe(II) was obtained by Fe(II) in chelated copper sequestration under near neutral pH condition (pH 7.70). The mechanism of Cu(II)-EDTA sequestration by Fe(II) was concluded as follows: 3Cu(II)-EDTA+7Fe(II)+9H2O → Cu(0)↓+ Cu2O↓(the major product)+2Fe2O3·H2O↓+3Fe(II)-EDTA +14H(+) Novel results strongly indicate that Cu(II) reductive transformation induced by surface Fe(II) was mainly responsible for chelated copper sequestration. Cu(0) generation was initially facilitated, and subsequent reduction of Cu(II) into Cu(I) was closely combined with the gradual increase of ORP (Oxidation-Reduction Potential). Cu-containing products were inherently stable, but Cu2O would be reoxidized to Cu(II) with extra-aeration, resulting in the release of copper, which was beneficial to Cu reclamation. Concentration diminution of Cu(II)-EDTA within the electric double layer and competitive adsorption were responsible for the negative effects of Ca(2+), Mg(2+). By generating vivianite, PO4(3-) was found to decrease surface Fe(II) content. This study is among the first ones to identify the indispensible role of reductive decomplexation in chelated copper sequestration. Given the high feasibility and reactivity, Fe(II) may provide a potential alternative in chelated metals pollution controlling.

Sustainable hydrogen production from electroplating wastewater over a solar light responsive photocatalyst

An environmentally friendly and sustainable photocatalytic hydrogen production system was successfully developed using EDTA in the wastewater as the photo-excited hole scavenger and a solar light responsive material as the photocatalyst.

Lamellar supramolecular materials based on a chelated metal complex for organic dye adsorption

The industrial poisonous waste chelated copper complex can be made into recyclable lamellar supramolecular materials which display excellent adsorption ability towards organic dyes.