Integrating integrated circuit wastewater into the metal catalyst supply chain

Abstract

The rapid growth of the integrated circuit (IC) industry has led to the generation of highly complex and challenging-to-treat wastewater streams. This work presents a sustainable paradigm for transforming metal-containing IC wastewater into efficient heterogeneous catalysts. As a proof of concept, Cu-rich IC wastewater is converted into a multifunctional Cu/SiO₂ catalyst via a simple ammonia-evaporation process, achieving up to 99.9% Cu recovery. The catalyst exhibits outstanding activity in the upcycling of various real-world polyethylene terephthalate (PET) wastes to p-xylene (PX) with near-quantitative yield (>99.9%), surpassing commercial Cu/SiO₂. The superior catalytic performance is attributed to the modulation of the catalyst structure by trace coexisting metals in the wastewater, which promote the formation of abundant Cu/CuO_x interfacial sites, facilitating H₂ dissociation and C–O bond activation. Furthermore, this strategy also enables the complete transformation of Cu species onto other supports to construct various Cu-based catalysts. Overall, this work establishes a new paradigm for valorizing IC wastewater, which can be extended to other metal-containing wastewaters (e.g., Ni, Co, Pt), in alignment with the principles of green chemistry and the circular economy.

Managing hazardous industrial wastewater remains a critical hurdle for sustainable manufacturing and environmental protection. This study converts metal-rich integrated circuit waste into high-performance catalysts that efficiently upcycle plastic pollution.

Introduction

Integrated circuits (ICs) constitute the foundation of the semiconductor industry, accounting for approximately 85% of the global semiconductor market. From 2020 to 2025, the annual compound annual growth rate of the global market size is 6.8%, and it is expected to exceed 720 billion US dollars by 2025. As the most widely used semiconductor components, ICs have attracted a global concentration of chip fabrication plants, printed circuit board (PCB) manufacturers, and related industries. IC fabrication is highly complex and relies on a wide array of chemical reagents, however, only a minimal portion of these chemicals remained on wafers, while the rest entered into wastewater. Before key manufacturing steps such as silicon oxidation, photolithography, epitaxy, diffusion, and lead evaporation, physical or chemical methods are employed to remove surface contaminants and native oxides from silicon wafers to meet stringent cleanliness standards^1–8. These processes consume a large amount of fresh water while generating a considerable amount of wastewater. An IC company can consume thousands of cubic meters of fresh water every day, equivalent to the annual consumption of a city of approximately 100,000 people, with a potential upward trend in the future⁹. Unlike traditional municipal and industrial wastewater, IC wastewater cannot be directly mixed and discharged with municipal or industrial wastewater systems. (For detailed discussions, see the Supplementary Information) IC wastewater serves as a significant source of heavy metals such as copper, which can bio-accumulate in living organisms, thereby posing a significant threat to ecosystem health^10,11. Consequently, a paradigm shift toward the resource recovery and valorization of IC wastewater is urgently required, repositioning it from an environmental burden to a valuable resource stream.

During IC manufacturing, wastewater streams enriched with metals are inevitably produced^12–14. For example, etching processes employ corrosive solutions to remove semiconductor materials or metal layers, resulting in wastewater containing Cu, Al, Fe, and Ni^15–18. Similarly, electroplating processes release solutions containing Ag, Au, and Cu directly into wastewater^19–21. Furthermore, the deposition of specific functional layers, such as resistive materials, further introduces noble metals such as Pt, Pd, and Ru into wastewater. Given the limited global reserves and high economic value of these metals, IC wastewater constitutes a substantial and underexploited metal resource, highlighting the critical importance of their efficient recovery and value-added utilization.

The predominant metallic species in IC wastewater are transition metals. Owing to their incompletely filled d orbitals, these metals can undergo reversible redox transformations and adopt multiple oxidation states, thereby stabilizing reaction intermediates or transition states^22–25. Such intrinsic characteristics enable effective mediation of electron transfer, activation of chemical bonds, reduction of reaction barriers, and selective control of reaction pathways, which underpins their widespread application as pivotal components in catalytic systems. Accordingly, the conversion of IC wastewater into high-value metal-based catalysts holds significant promise and represents a new paradigm for the valorization of such wastewater. However, given the complexity of metal species present in wastewater and the fact that only specific metal components exhibit catalytic activity in targeted reactions, this direction remains highly challenging, and no relevant studies have yet been reported in this emerging direction.

Polyethylene terephthalate (PET) is the most abundant polyester plastic in the world²⁶. The global annual production of PET is nearly 70 million tons, accounting for approximately 8% of the global plastic output and about 12% of the total solid plastic waste^27,28. Post-consumer PET waste poses a serious environmental challenge^29–32. Currently, the recycling rate of PET is less than 10%^33,34, and its catalytic depolymerization into value-added products has emerged as the most effective recycling strategy³⁵. Among the possible routes, PET hydrogenolysis to p-xylene (PX) is of particular significance, as PX serves not only as a gasoline additive and antifreeze component but also as a key precursor for PET monomer synthesis³⁶. At present, the conversion of PET to PX still suffers from the high cost of noble metal catalysts and the undesired side reactions, such as C–C cleavage and benzene ring hydrogenation³¹. Therefore, developing efficient catalysts for the selective conversion of PET to PX is of great significance.

Here, we propose a new paradigm for valorizing metals in IC wastewater into metal-based catalysts (Fig. 1). The first example of converting Cu-rich IC wastewater into a multifunctional Cu/SiO₂ catalyst is demonstrated, with the obtained catalyst exhibiting exceptional catalytic performance in waste plastic upcycling. The catalyst was prepared by a simple ammonia-evaporation method on commercial SiO₂, achieving a Cu recovery efficiency of up to 99% from IC wastewater. Remarkably, the catalyst enabled the conversion of waste polyethylene terephthalate (PET) into high-value p-xylene (PX) with near-quantitative yield (> 99.9%), even outperforming the commercial Cu/SiO₂ catalyst. The superior performance is primarily attributed to the overall modulation by coexisting metal species (e.g., Na, Zn) in the wastewater, which generates abundant Cu/CuO_x interfacial active sites that facilitate hydrogen dissociation and C–O bond activation. Moreover, this catalyst demonstrates broad applicability toward the upcycling of various real-world plastics. This approach establishes a new paradigm for integrating IC wastewater into the metal catalyst supply chain can be extended to the valorization of integrated circuit wastewater containing other transition metals (e.g., Ni, Co, Pt), offering promising avenues for sustainable metal recovery and low-cost preparation of metal catalysts.

Fig. 1. Schematic illustration of integrating IC wastewater into the metal catalyst supply chain.

IC refers to an integrated circuit.

Results

Transforming IC wastewater into IC-Cu/SiO₂ catalyst

The untreated IC wastewater was obtained from an IC engineering facility in Guangdong Province, China. The wastewater was collected as a mixed effluent generated during the production of printed circuit boards. The metallic cation composition was quantitatively determined using inductively coupled plasma optical emission spectroscopy (ICP-OES). The dominant constituents were Cu (10,350 ppm), Na (26,700 ppm), Zn (180 ppm), and K (140 ppm). Minor elements, including Ca, Fe, Co, and Ni, were detected at concentrations below 100 ppm, while other elements were present at concentrations below 10 ppm and considered negligible. Cu 2p XPS analysis after removing the water from the IC wastewater via evaporation under vacuum conditions revealed that the Cu species remained in the Cu²⁺ state (Supplementary Fig. 1). The total organic carbon (TOC) content was determined to be 10% using a TOC analyzer, and all ion concentrations were quantified by ion chromatography (Supplementary Table 1).

A Cu/SiO₂ catalyst derived from IC wastewater (IC-Cu/SiO₂) was synthesized by a simple ammonia evaporation method using low-cost commercial SiO₂ as the support (Fig. 2a), targeting a Cu loading of 20 wt%. The treated wastewater became clear and transparent after resource recovery (Fig. 2d), indicating substantial Cu removal. ICP-OES analysis confirmed a Cu loading of ~20 wt% in IC-Cu/SiO₂ (19.0%, 19.3%, and 21.3% in triplicate). Meanwhile, the residual Cu concentration in the effluent decreased to 12.12 ppm (Fig. 2b), corresponding to a recovery efficiency of 99.9%. Furthermore, the utilization efficiencies of Na, Zn, and K reached 99.8%, 99.3%, and 74.5%, respectively. XPS and EDS observations on IC-Cu/SiO₂ revealed no detectable Cl species (Supplementary Figs. 2, 3), indicating that the chloride ions in the IC wastewater do not deposit on the catalyst surface. Furthermore, the Cl ion concentration in the solution was monitored before and after the ammonia evaporation process (Supplementary Table 2). Titration results showed that the Cl ion content in the solution remained essentially unchanged, further indicating that the Cl ions in the IC wastewater are not deposited on the catalyst surface.

Fig. 2. The preparation process of the IC-Cu/SiO₂.

a Schematic diagram of IC-Cu/SiO₂ catalyst preparation. b The content and removal rate of metal ions in IC wastewater before and after the catalyst preparation. c XRD patterns of IC-Cu/SiO₂. d Untreated IC wastewater (left) and wastewater filtered after preparing the catalyst (right). e, f SEM image of IC-Cu/SiO₂ and Cu/SiO₂. g TEM images of IC-Cu/SiO₂. h EDS mapping profiles of IC-Cu/SiO₂.

Next, various characterizations were employed to determine the structure of IC-Cu/SiO₂. The XRD patterns of all samples were refined using the MDI-Jade software, the XRD patterns (Fig. 2c and Supplementary Fig. 4) exhibited characteristic peaks corresponding to Cu (2θ = 43.297°, 50.433°, and 74.13°; PDF #04-0836) and Cu₂O (2θ = 36.738°, 42.611°, 62.444°, and 74.131°; PDF #05-0667). The crystallinity of each sample was subsequently calculated. The interplanar lattice spacing and crystallite sizes of Cu and Cu₂O were calculated using the Bragg equation and Scherrer equation (Supplementary Table 3). The corresponding crystallinity values and R-factors (fitting errors) are summarized in Supplementary Table 4. Compared with Cu/SiO₂, IC-Cu/SiO₂ and CuNa/SiO₂ exhibit lower crystallinity, which suggests a higher dispersion of Cu species on the catalyst surface, likely due to enhanced metal–support interactions. Scanning electron microscopy (SEM) images revealed that IC-Cu/SiO₂ (Fig. 2e) exhibited a rougher surface morphology and a higher density of small particles compared with Cu/SiO₂ catalyst prepared from commercial CuCl₂ (Fig. 2f). This is likely attributable to the incorporation of heterogeneous elements from the wastewater, which could potentially induce lattice distortion. The transmission electron microscope images (TEM) (Supplementary Fig. 5) show that the average particle sizes of IC-Cu/SiO₂ and Cu/SiO₂ are 3.98 ± 0.87 nanometers and 6.22 ± 1.00 nanometers, respectively, with the latter size being significantly larger than the former. TEM and EDS mapping (Fig. 2g, h) confirmed the uniform dispersion of Cu and Na on SiO₂ within the IC-Cu/SiO₂.

Catalytic Performance in the Hydrogenolysis of PET to PX

The performance of the IC-Cu/SiO₂ catalyst in the conversion of PET to PX was evaluated. Encouragingly, highly efficient PET hydrogenolysis was achieved under comparable conditions (230 °C, 2.5 MPa H₂, 5 h), yielding PX with 81.5% yield, which further increased to 99.9% after 8 h over IC-Cu/SiO₂. This performance surpasses that of the Cu/SiO₂ catalyst prepared from commercial CuCl₂ (Fig. 3a). The PET feedstocks used in the performance test were real, shredded PET plastic bottle (Supplementary Fig. 6). Before the reaction, the solution contained only the catalyst and the PET bottle fragments, after the reaction, PET was no longer visible, and only black catalyst powder remained in the solution (Fig. 3a). To investigate the influence of other elements in IC wastewater on the catalytic performance, three Cu/SiO₂ catalysts (CuNa/SiO₂, CuZn/SiO₂, and CuK/SiO₂) containing other metals were prepared using the same method. ICP-OES confirmed that the actual (ACT) metal loadings in these catalysts were consistent with the nominal (NOM) loading of the catalyst from IC wastewater composition (Fig. 3b). CuNa/SiO₂ exhibits significantly enhanced catalytic performance compared to Cu/SiO₂. Although the presence of Na, Zn, and K could influence the catalytic activity of Cu/SiO₂³⁵, the concentrations of Zn and K in the IC wastewater are relatively low. Consequently, the improvements in catalytic performance observed for CuZn/SiO₂ and CuK/SiO₂ are marginal. These findings suggest that the synergistic regulation effect of multiple elements present in the IC wastewater plays a crucial role in enhancing the catalytic performance of IC-Cu/SiO₂.

Fig. 3. Catalytic performance and possible reaction pathway in hydrogenolysis of PET to PX.

a Catalytic performance of various catalysts. b The metal loadings of various catalysts. c The stability of IC-Cu/SiO₂. Reaction conditions: 0.1 g catalyst, 0.1 g PET, 10 mL of 1,4-dioxane, 600 rpm, 230 °C, 2.5 MPa H₂, 5 h. d, e Effect of H₂ pressure and temperature. f Influence of Cu²⁺ concentration in IC wastewater on catalyst performance. 20¹: Stirring time 6 hours. 20²: Stirring time extend to 12 h. g The catalytic performance comparison of reported catalysts. *: on CuNa/SiO₂, hydrogen was not added beforehand, and the pressure was derived from the hydrogen production through methanol reforming. h GC spectra of the reaction results. i Possible reaction pathway for the conversion of PET to PX over IC-Cu/SiO₂. Reaction conditions: 0.1 g catalyst, 0.1 g substrate, 10 mL 1,4-dioxane, 600 rpm, 230 °C, 2.5 MPa H₂, 1.5 h.

The stability of IC-Cu/SiO₂ was further confirmed through six recycle experiments (Fig. 3c). The yield of PX remained consistently stable in six cycles, highlighting the excellent stability of IC-Cu/SiO₂. We systematically optimized the reaction conditions using orthogonal experiments to determine the optimal temperature, hydrogen pressure, and reaction time. Initially, under conditions of 230 °C and 2.5 MPa H₂, the temporal evolution of the PX yield was monitored. The results indicated that at 230 °C and 2.5 MPa H₂, a reaction time of 8 h afforded a PX yield exceeding 99.9% (Supplementary Fig. 7). Subsequently, with H₂ pressure fixed at 2.5 MPa, the PX yield was evaluated at various reaction temperatures. The yield reached a maximum at 230 °C; lower temperatures reduced the reaction rate, whereas higher temperatures increased energy consumption without further enhancing the yield (Fig. 3d). Similarly, with the temperature maintained at 230 °C, varying the H₂ pressure revealed that the PX yield increased with pressure up to 2.5 MPa, beyond which additional pressure provided no significant improvement (Fig. 3e). GC–MS analysis of the liquid product obtained under low-pressure conditions confirmed PX as the sole product, with no detectable intermediates (Supplementary Fig. 8). Moreover, it was observed that IC-Cu/SiO₂ could catalyze the conversion of PET to PX at lower temperatures and H₂ pressures; extending the reaction time under these conditions still enabled the PX yield to reach 99.9% (Supplementary Table 5). These results highlight its outstanding catalytic activity and selectivity, as well as a wide operational window for reaction conditions, demonstrating its great potential for industrial applications. Based on these observations, the optimized reaction conditions were determined to be 2.5 MPa H₂ and 230 °C, achieving a PX yield of 99.9% within 8 h. Given the significant fluctuations in the concentration of IC wastewater, the Cu²⁺ concentration can reach up to 200,000 mg/L at its peak³⁷. To address this variability, we developed corresponding synthesis and regulation strategies to ensure efficient catalytic performance. (For more details, see the Supplementary Information below Supplementary Table 6 and 7). Under identical synthesis conditions, IC-Cu/SiO₂ catalysts were prepared using IC wastewater with varying Cu²⁺ concentrations. It was observed that, when low-concentration IC wastewater was used, prolonging the stirring time enhanced the copper loading on the SiO₂ support. For instance, at a Cu²⁺ concentration of 20 mg/L, extending the stirring time to 12 h effectively increased the copper loading, yielding IC-Cu/SiO₂ catalysts with excellent catalytic performance (Fig. 3f and Supplementary Table 6). Furthermore, IC-Cu/SiO₂ outperformed most of the previously reported catalysts and was comparable to the best-performing ones. (Fig. 3g and Supplementary Table 8)^{31,35,36,38–46}. (For detailed discussion, see the Supplementary Information below Supplementary Table 8.)

To evaluate the purity of the product PX, various characterizations were performed. TGA analysis of the spent catalyst after 6 h confirmed complete conversion of PET with no undecomposed polymer residue mass (Supplementary Fig. 9). FTIR spectra of the catalyst before and after reaction (Supplementary Fig. 10) showed no discernible changes, confirming structural stability and the absence of organic residue accumulation. GC analysis of the liquid product (excluding solvent and internal standard peaks) revealed a single peak corresponding to PX (Fig. 3h). These findings provide compelling evidence for the near-quantitative production of PX. For the PET conversion into PX, side reactions such as C-C bond cleavage and benzene ring hydrogenation result in unsatisfactory PX selectivity³¹. Our designed IC-Cu/SiO₂ catalyst enables the successful realization of near-quantitative PX production. To gain a more comprehensive understanding of the catalytic process, we performed GC analysis on the gas products generated during the hydrogenolysis of PET. The results (Supplementary Fig. 11) show that a significant amount of ethane and trace amounts of methane were produced. The formation of ethane primarily stems from the complete hydrogenolysis of the ethylene glycol units within PET, while the trace methane is attributed to excessive C-C bond cleavage in the ethyl units. No other gas products, such as CO or CO₂, were detected, indicating that the aromatic units did not undergo any decarboxylation or decarbonation, as evidenced by the high yield of PX. This indicates that IC-Cu/SiO₂ can selectively convert PET into PX while avoiding common undesired side reactions.

To elucidate the degradation pathway of PET over IC-Cu/SiO₂, we conducted PET hydrogenolysis under mild conditions, successfully capturing a weak signal for 4-methylbenzyl alcohol (Supplementary Fig. 12). Furthermore, the conversion dimethyl terephthalate (DMT) as a model substrate, was carried out under even milder conditions, generating intermediates such as 4-methylbenzyl alcohol and methyl 4-methylbenzoate (Supplementary Fig. 13). These results confirm that the reaction initially involves ester bond cleavage, yielding the intermediates (4-methylbenzyl alcohol and ethyl 4-methylbenzoate), which subsequently undergo hydrogenolysis to produce PX. To verify this pathway, we investigated the conversions of model intermediates, including 4-methylbenzyl alcohol, ethyl 4-methylbenzoate, dimethyl terephthalate, and terephthalic acid. The results indicated that 4-methylbenzyl alcohol, ethyl 4-methylbenzoate, and dimethyl terephthalate could all be converted to PX over IC-Cu/SiO₂, with the highest yield observed for 4-methylbenzyl alcohol. In contrast, terephthalic acid showed negligible conversion. These findings support the pathway where PET hydrogenolysis proceeds via ester bond hydrogenation to form 4-methylbenzyl alcohol, which further undergo the hydrogenolysis to produce PX, rather than via a terephthalic acid intermediate pathway (Fig. 3i).

Catalyst characterizations

A series of characterizations were performed to elucidate the geometric and electronic structures of the IC-Cu/SiO₂ catalyst. ICP-OES confirmed that the actual Cu loading of IC-Cu/SiO₂ was highly consistent with the nominal value (Fig. 3b). Transmission electron microscopy (TEM) images of IC-Cu/SiO₂ (Fig. 4a, b) revealed its overall morphology, while HR-TEM analysis (Fig. 4c) provided detailed structural information. The measured lattice spacings of 0.181 nm, 0.209 nm, 0.212 nm, and 0.243 nm correspond to the (200) and (111) crystal planes of metallic Cu, and the (200) and (111) crystal planes of Cu₂O, respectively. Two distinct interfacial structures were observed: the interface formed between metallic Cu (111) and Cu₂O (111) (Interface I), and the interface formed between metallic Cu (111) and Cu₂O (200) (Interface II).

Fig. 4. Catalyst characterization.

a–c HR-TEM images of IC-Cu/SiO₂, (d) H₂-TPR profiles. e Cu LMM X-ray induced Auger electron spectroscopy (XAES) spectra. f Cu L-edge sXAS. g O K-edge sXAS. h EPR spectra of IC-Cu/SiO₂ and Cu/SiO₂. i The IR spectra of adsorbed pyridine.

The chemical environment of copper was further investigated using H₂-TPR, XPS, XAES, and sXAS (Fig. 4d–g). The H₂-TPR profiles (Fig. 4d) of all three samples exhibit a single reduction peak, which can be attributed to the reduction of copper silicate⁴⁷. The copper silicate structure in IC-Cu/SiO₂ (unreduced) was further confirmed by TEM and XRD analyses (Supplementary Figs. 14, 15). Notably, the reduction peak temperatures of CuNa/SiO₂ and IC-Cu/SiO₂ are higher than that of Cu/SiO₂, indicating that the copper silicate phase (Cu₂Si₂O₅(OH)₂, Supplementary Fig. 16) formed via the ammonia evaporation method for IC wastewater-derived catalysts possesses a denser structure compared to the copper silicate in catalysts prepared from CuCl₂ (Supplementary Fig. 17), accompanied by stronger metal–support interactions. Such enhanced interactions facilitate a more uniform dispersion of copper species and the generation of a greater number of interfacial sites. Consistently, XRD analysis (Supplementary Fig. 16) reveals that IC-Cu/SiO₂ (unreduced) exhibits copper silicate with lower crystallinity, smaller nanoparticles, and a more uniform particle size distribution, further corroborating the presence of stronger metal–support interactions (see Supplementary Information, Supplementary Fig. 18, for additional discussion about stronger metal–support interactions). Cu XPS (Supplementary Fig. 19) and Cu LMM spectra (Fig. 4e) show the presence of Cu²⁺ peak at 940-950 eV, indicating incomplete reduction of copper silicate precursor. Because the binding energies of Cu⁰ and Cu⁺ species are closely spaced, Cu LMM X-ray induced Auger electron spectroscopy (XAES) was employed to quantify the Cu⁺/Cu⁰ ratio. IC-Cu/SiO₂ exhibited a higher Cu⁺/Cu⁰ ratio (1.28) than that of Cu/SiO₂ (0.29), suggesting that the structurally dense copper silicate derived from wastewater precursors was not easily reduced to Cu⁰. This can be ascribed to the anchoring effect of strong metal–support interactions on the Cu species in IC-Cu/SiO₂, consistent with the findings from TEM and H₂-TPR. To further elucidate the critical role of Cu⁺ as an active site, IC-Cu/SiO₂ catalysts were prepared via the impregnation (IM), coprecipitation (CP), and hydrothermal (HT) methods. Following identical reduction treatments, catalytic performance tests (Supplementary Table 9) revealed that only IC-Cu/SiO₂ (HT) achieved a PX yield of 4.6%, whereas the other catalysts produced no PX. Taking IC-Cu/SiO₂ (IM) as an example, Auger electron spectroscopy (AES) analysis confirmed the absence of Cu⁺ species on the catalyst surface (Supplementary Figs. 20, 21). The lack of Cu⁺ species accounts for the observed inactivity, highlighting the essential role of Cu⁺ sites in the activation of C-O bonds in PET. Furthermore, soft X-ray absorption spectroscopy (sXAS) measurements (Fig. 4f) show that the Cu L-edge spectra contained two distinct features corresponding to orbital transitions from 2p_3/2 to 3 d (L₃) and from 2p_1/2 to 3 d (L₂). Compared with Cu/SiO₂, both L₃ and L₂ peaks of IC-Cu/SiO₂ shifted toward lower energy, indicating decreased electron density around Cu sites and a greater tendency to stabilize higher oxidation states, consistent with XAES results (Fig. 4e)⁴⁸. In short, the above findings suggest that, in the IC-Cu/SiO₂ catalyst, strong metal–support interactions promote high dispersion of Cu species and give rise to abundant Cu/CuO_x interfacial sites.

To gain further insight into the microenvironment of the catalyst, O K-edge X-ray absorption spectroscopy, EPR, and Py-FTIR measurements were conducted. In the O K-edge spectra (Fig. 4g), a new peak appears at ~ 534.9 eV for IC-Cu/SiO₂ and CuNa/SiO₂, attributable to oxygen vacancies, which were negligible in other catalysts⁴⁹. Electron paramagnetic resonance (EPR, Fig. 4h) further confirmed the presence of oxygen vacancies, showing a characteristic signal at g = 2.003, associated with unpaired electrons localized at oxygen-deficient sites⁵⁰. The significantly stronger signal intensity for IC-Cu/SiO₂ compared with Cu/SiO₂ indicated a higher concentration of oxygen vacancies. In general, an increased concentration of oxygen vacancies may render CuO_x species more coordinatively unsaturated, thereby enhancing their Lewis acidity. To verify this, pyridine-FTIR was employed to investigate the evolution of Lewis acid sites (Fig. 4i). The peaks at approximately 1438 and 1580 cm^-1 represent Lewis acid sites, the peak at ~ 1596 cm⁻¹ corresponds to strong Lewis acid sites, and the peak at ~ 1480 cm^-1 represents a mixture of Lewis acid and Brønsted acid sites. Notably, all peaks corresponding to Lewis acid sites exhibit larger peak areas on IC-Cu/SiO₂ than Cu/SiO₂, clearly indicating a higher density of Lewis acid sites⁵¹.

In summary, all the aforementioned characterizations of the geometric and electronic structures demonstrate that the IC-Cu/SiO₂ catalyst exhibits higher dispersion of Cu species due to strong metal-support interactions, resulting in an increased number of Cu⁰–CuO_x interfacial sites. Furthermore, its CuO_x sites possess a greater abundance of oxygen vacancies and higher coordinative unsaturation. This structural feature is likely attributable to the synergistic regulation by various metal elements present in the wastewater, with the substantial presence of Na species playing a particularly significant role. Given that the concentration of Na in the IC wastewater employed in this study was considerably higher than those of Zn and K, the regulatory effect of Na was more pronounced. Nevertheless, this does not imply the absence of regulatory contributions from Zn and K. A detailed discussion of the effects of Zn and K is provided in the Supplementary Information (see Supplementary Figs. 22, 23). Subsequently, we focus on elucidating the underlying mechanism by which these structural characteristics endow the catalyst with its distinctive performance in the hydrogenolysis of PET to PX.

Unique catalytic roles of IC-Cu/SiO2

First, the adsorption–desorption behaviors of the substrate and product over IC-Cu/SiO₂ and Cu/SiO₂ were investigated. Using ethyl 4-methylbenzoate as a model molecule, the time-dependent curves show that IC-Cu/SiO₂ consistently exhibited higher activity (Fig. 5a). More importantly, the PX yield over IC-Cu/SiO₂ increased almost linearly with time, reaching its maximum after 10 h. On the contrary, Cu/SiO₂ reached a PX yield of ~ 50% at 6 h, after which the rate of increase slowed significantly, indicating a competitive adsorption between PX and the substrate. Temperature-programmed desorption (TPD) of methyl ethyl benzoate on both catalysts (Fig. 5b) revealed that the desorption peak area of IC-Cu/SiO₂ was 1.5-fold higher than that of Cu/SiO₂, suggesting its more active sites for the adsorption of methyl ethyl benzoate. According to previous reports, oxygen-containing substrates within plastics are typically adsorbed on Lewis acid sites. Given that IC-Cu/SiO₂ possesses a higher density of CuO_x Lewis acid sites, it accordingly provides more adsorption sites for the substrate. TPD of PX further highlighted that PX adsorption on IC-Cu/SiO₂ was weaker, which is beneficial for its rapid desorption and promotes continuous catalytic turnover (Fig. 5c). Conversely, PX adsorption on Cu/SiO₂ was much stronger, particularly in the high-temperature pronounced adsorption region, suggesting significant competitive adsorption between product and substrate. The accumulation of PX significantly inhibits the reaction process, consistent with the observed reaction curve.

Fig. 5. Catalytic mechanism.

a Time profile of hydrogenolysis. b Ethyl 4-methylbenzoate-TPD profiles. c PX-TPD profiles. d PX production efficiency under different H₂ pressure and 4-methylbenzoate concentration. Reaction conditions: 0.03 g catalyst, 0.1 g ethyl 4-methylbenzoate, 10 mL of 1,4-dioxane, 600 rpm, 230 °C, 5 min, H₂ pressure ranging from 1.5 MPa to 2.5 MPa; 0.03 g catalyst, 10 mL of 1,4-dioxane, 600 rpm, 230 °C, 5 min, 2.5 MPa H₂, weight of ethyl 4-methylbenzoate ranging from 1.0 g to 2.5 g. e H₂-TPD profiles. f–h In situ FTIR spectra of ethyl 4-methylbenzoate adsorption and desorption under Ar on IC-Cu/SiO₂ and Cu/SiO₂. i In situ methyl benzoate-conversion FTIR spectra under 10% H₂/Ar on IC-Cu/SiO₂ and Cu/SiO₂. j Proposed catalytic mechanism on IC-Cu/SiO₂.

Since the active sites in the IC-Cu/SiO₂ are both CuO_x and Cu⁰ species, their precise quantification remains challenging, and thus, the reaction orders with respect to substrate and H₂ cannot be directly determined. Nevertheless, under the applied kinetic conditions, systematic studies of product yield as a function of substrate concentration and hydrogen pressure (Fig. 5d) revealed comparable effects, as evidenced by similar fitted slopes. This finding indicates that the hydrogen partial pressure and substrate concentration have similar important influences on the catalytic performance.

Subsequently, H₂-TPD was conducted to explore the H₂ adsorption abilities of both catalysts. (Fig. 5e) They displayed two distinct desorption peaks, where the low-temperature peak was attributed to hydrogen adsorption on Cu⁰ species, while the high-temperature peak corresponded to the desorption of hydrogen spilled over onto CuO_x species. Importantly, the high-temperature desorption peak of IC-Cu/SiO₂ appeared at a higher temperature, indicating that the spilled-over hydrogen species were more strongly stabilized, thereby facilitating the spillover process. Previous studies have reported that oxygen vacancies play a crucial role in promoting hydrogen spillover, as these electron-rich defects can effectively adsorb and stabilize hydrogen atoms, serving as anchoring sites for their migration from metallic centers⁵². Consequently, the higher density of oxygen vacancies surrounding CuO_x in IC-Cu/SiO₂ is particularly favorable for hydrogen spillover. It is well recognized that during substrate adsorption and activation on CuO_x, active hydrogen species originate from dissociation on Cu⁰ species and subsequently migrate via spillover to assist C-O cleavage⁵³. Thus, the enhanced hydrogen spillover capability of IC-Cu/SiO₂ is beneficial for driving the reaction forward.

To gain a deeper understanding of the catalytic mechanism at the molecular level, in situ FTIR spectroscopy experiments were conducted using methyl benzoate as a probe molecule (Fig. 5f–i). The characteristic band at 1729 cm⁻¹ belongs to the stretching vibration of C = O, while the peaks at 1278 cm⁻¹ and 1110 cm⁻¹ correspond to the asymmetric and symmetric stretching vibrations of C-O, respectively (Fig. 5f)⁵⁴. It is noteworthy that the three bands on IC-Cu/SiO₂ show stronger intensities than on Cu/SiO₂, indicating a higher density of active sites. Temperature-programmed in-situ FTIR of ethyl 4-methylbenzoate adsorption and desorption on both catalysts shows significant vibrational shifts: as the temperature increases, the C-O band exhibits a red shift, whereas the C = O band undergoes a significant blue shift (Fig. 5g, h). This reverse shift behavior strongly indicates that the C-O bond is preferentially adsorbed and activated rather than the C = O bond on both catalysts. The preferential activation of the C-O bond alters the electronic environment of adjacent functional groups, leading to an enhancement (blue shift) of the C = O vibration. Importantly, a new peak appeared at 1694 cm⁻¹ on IC-Cu/SiO₂, which coincides with the infrared signature of the aldehyde species⁵⁵, and its intensity increased with temperature (Fig. 5g). The appearance of the signal indicates the formation of aldehyde-like structures during the ester bond activation, providing important evidence for the activation and cleavage of the C-O bond. In contrast, no corresponding bands were observed on Cu/SiO₂, indicating that IC-Cu/SiO₂ has a stronger ability to activate and cleave the C-O bond in the ester group. This provides compelling mechanistic evidence, demonstrating that on IC-Cu/SiO₂, the reaction is initiated by C–O activation, leading to the formation of aldehyde-like intermediates. Upon subsequent hydrogen introduction, hydrogenolysis was triggered. As the reaction proceeded, the characteristic vibration signals of the ester group gradually weakened, indicating a smooth and continuous conversion (Fig. 5i). However, no detectable signal corresponding to the aldehyde intermediate was observed during in situ hydrogenolysis, suggesting that these intermediates were highly transient and rapidly converted into downstream products, making them difficult to capture under in situ conditions.

Based on the above results, the catalytic mechanism on IC-Cu/SiO₂ is proposed (Fig. 5j). This process initiates with the adsorption and activation of the C-O bond in PET at the Cu/CuO_x interface, particularly on CuO_x sites enriched with oxygen vacancies. Subsequently, H₂ dissociates on Cu⁰, generating active H* species that spill over to the adjacent Cu/CuO_x interface. These H* species attack the activated C-O bond, leading to their cleavage and the formation of aldehyde intermediates. The C = O group is further activated and hydrogenated at the Cu/CuO_x interface to form hydroxyl intermediates, and then through the cleavage of the C-O bond to produce the product PX. Finally, PX desorbs from the catalyst surface, completing the catalytic cycle.

IC-Cu/SiO2 for real-world plastic waste conversion

To assess the practical applicability of IC-Cu/SiO₂, its performance was systematically evaluated in the hydrogenolysis of various post-consumer PET waste and PET materials containing common additives (Supplementary Fig. 24 and Supplementary Table 10). After simple shearing, all tested feedstocks were effectively converted into PX over IC-Cu/SiO₂ catalyst (Fig. 6a). To investigate the influence of typical additives in waste plastics, a series of PET conversions containing different representative compounds were investigated (Fig. 6b)⁵⁶. Most additives exhibit negligible effects on catalytic activity, with PX yields maintaining above 99.9%, while a few induced only slight inhibition, still maintaining yield above 90.0%. Furthermore, IC-Cu/SiO₂ demonstrates remarkable potential for the selective conversion of PET in mixed plastics, achieving high selectivity toward PX without interference from coexisting polymers. Conversions were performed using common PET-based mixed plastic systems, including 1) PET/PE and 2) PET/PP. Across six PET/PE and six PET/PP combinations, PX yields exceeded 98% and 90%, respectively (see Supplementary Information, Supplementary Table 11, for details). These results clearly demonstrate the robustness and impurity tolerance of IC-Cu/SiO₂ under realistic conditions.

Fig. 6. Various plastic conversions and future prospects.

a The direct hydrogenolysis of real-world PET plastics. Reaction conditions: 0.1 g IC-Cu/SiO₂, 0.1 g of PET plastics, 10 mL of 1,4-dioxane, 230 °C, 2.5 MPa H₂, 600 rpm, 12 h. b The direct hydrogenolysis of PET with additives. Reaction conditions: 0.1 g IC-Cu/SiO₂, 0.1 g of PET plastics, 5 wt% additives, 10 mL of 1,4-dioxane, 230 °C, 2.5 MPa H₂, 600 rpm, 12 h. c–e EDS spectroscopy mapping profiles of IC-Cu/Al₂O₃, IC-Cu/ZrO₂, IC-Cu/C.

In order to further evaluate the universality of IC wastewater-derived catalysts, additional catalysts were prepared using different supports. IC wastewater was loaded onto γ-Al₂O₃, ZrO₂ and activated carbon, and then treated by the impregnation method to prepare the IC-Cu/Al₂O₃, IC-Cu/ZrO₂, and IC-Cu/C catalyst. SEM-EDS analysis confirmed the uniform dispersion of elements, particularly Cu, across the catalyst surfaces (Fig. 6c–e). Moreover, XPS characterization verified the successful incorporation of Cu from IC wastewater into the surface of all four catalysts (Supplementary Figs. 25–27). These results unequivocally demonstrate that the valorization of IC wastewater into functional catalytic materials is not only technically feasible but also broadly applicable across diverse support systems.

Despite the promising potential of this strategy, several limitations remain. In practical applications, further research is required to optimize the catalyst preparation method to accommodate variations in IC wastewater composition and to enhance overall performance for diverse wastewater streams. When the concentrations or types of metal elements in the wastewater are insufficient to achieve effective catalytic performance, the addition of trace amounts of specific metals could be employed to optimize the composition and substantially enhance activity.

Importantly, this approach extends beyond conventional waste management by establishing a paradigm for converting hazardous industrial effluents into value-added catalyst resources. In the future, it could be applied to other metal-containing wastewaters, with the resulting catalysts being used in additional catalytic reactions. Machine learning could also be employed to establish a database linking IC wastewater–derived catalysts with their corresponding catalytic applications. Furthermore, the regulatory effects of minor metals on the primary active species require detailed investigation to accurately elucidate the surface properties of IC-derived catalysts. Conversely, when a minor element serves as the main active site, the influence of abundant metals on its activity should also be assessed. Finally, IC wastewater could be combined with other waste streams, such as biomass or sludge, to prepare advanced catalysts, enabling the synergistic conversion of multiple waste sources and promoting a circular approach to waste valorization.

By redirecting IC wastewater from conventional sewage treatment toward advanced catalyst fabrication, this approach integrates environmental remediation with resource recovery, embodying the principles of green chemistry and circular economy. Such IC wastewater-derived catalysts not only provide a sustainable pathway for mitigating the dual challenges of electronic waste and plastic pollution but also open new opportunities for designing cost-effective, scalable, and environmentally benign catalytic systems. Future investigations into their practical catalytic applications will further consolidate their potential as a disruptive solution for sustainable chemical manufacturing and global environmental governance.

Discussion

In summary, we have developed a new paradigm for integrating IC wastewater into the metal catalyst supply chain. We presented the first example by using IC wastewater as a raw material to develop an IC-Cu/SiO₂ catalyst. This catalyst utilizes the rich Cu/CuO_x interfacial sites to achieve ultra-high selectivity in the conversion of PET into PX, reaching a performance level comparable to that of state-of-the-art metal catalysts. The performance enhancement is attributed to the regulation of other metal species present in the wastewater, which generate abundant Cu/CuO_x interface active sites and abundant oxygen vacancies. This study underscores the broad applicability of the IC wastewater-derived catalyst to diverse real-world plastics and reveals the great potential of completely transferring Cu species onto various supports to develop a wide range of Cu-based catalysts. The IC wastewater-derived catalyst enables the nearly quantitative conversion of waste PET into PX while achieving a 99% metal recovery rate from IC wastewater. This approach marks a substantial innovation in the synergistic design of plastic waste recycling, IC wastewater reutilization, and metal catalyst fabrication. Furthermore, this paradigm offers a sustainable and low-cost pathway for resource recovery and catalyst synthesis, opening new avenues toward enhanced environmental and economic sustainability.

Methods

Preparation of catalysts

The IC-Cu/SiO₂ catalyst was prepared by a simple ammonia vaporization method. Using integrated circuit wastewater and SiO₂ as precursors, the integrated circuit wastewater was diluted to an appropriate concentration, SiO₂ was added, and the mixture was stirred for 10 min. An appropriate amount of ammonia water was added, at this point, the suspension pH was 11-12, and it was stirred for 6 h. The suspension was transferred to a water bath at 80 °C, and the ammonia in the suspension was evaporated until the pH value was 6-7. The sample was washed three times with 1000 mL of deionized water, dried overnight at 80 °C, and then fired at 450 °C for 4 h.

The same method as that used for IC-Cu/SiO₂ was adopted to synthesize Cu/SiO₂, CuNa/SiO₂, CuK/SiO₂, and CuZn/SiO₂. However, the integrated circuit wastewater was changed into solutions of CuCl₂, NaCl, KCl, and ZnCl₂.

All catalysts should be reduced at 350 °C for 4 h under flowing H₂ (10%H2-Ar mixed gas) before reaction.

Catalytic test and product analysis

The detailed reaction conditions are described in the figure captions and table footnotes. In a typical reaction with PET conversion as an example, 0.1 g of PET balls, 0.1 g of catalyst, and a solvent mixture of 10 mL of 1,4-dioxane were loaded into a stainless-steel autoclave reactor in a 50 mL stainless steel batch reactor equipped with a Polytetrafluoroethylene (PTFE) liner and magnetic rotor. After the reactor was purged with H₂ three times and charged to the target H₂ pressure (2.5 MPa), the reaction was conducted at the target temperature (230 °C) with a magnetic stirring speed of 600 rpm. Upon completion, the reactor was cooled naturally. The quantitative analysis of reacting products was performed using gas chromatography (GC-2060) with a flame ionization detector equipped with HP-5 capillary columns. The column temperature began at 50 °C (held for 5 min) and was then increased to 280 °C at a heating speed of 10 °C min⁻¹ (held for 10 min); the total running time was 50 minutes. The liquid solution was separated from the solid catalyst by centrifugation and was directly analyzed when 1,4-dioxane was used as a solvent. Biphenyl was used as an internal standard for the quantification of the liquid products. The PX yield was calculated following the Eq. (1):

$$PXyield=\frac{n_{PX}\left(mol\right)}{n_{aromaticringmolesofPET}\left(mol\right)}\times 100\%$$ 1

Characterization

The crystal structure of the catalyst was analyzed via X-ray diffraction with Cu Kα (λ = 0.15406 nm) radiation (XRD, D8 ADVANCE, Bruker Co., Germany) at 40 kV and 40 mA. The morphology of catalysts was examined by transmission electron microscopy (TEM) with an FEI Talos 200X (USA) field emission electron microscope. The actual Cu loading in the sample was detected by a Thermo Scientific™ iCAP™ PRO XP ICP-OES. Raman spectra were recorded using a HORIBA XploRA™ PLUS equipped with an Ar laser (532 nm wavelength). Surface composition and chemical states of the products were characterized by X-ray photoelectron spectroscopy (XPS, PHI 5000 Versaprobe III, Japan) equipped with monochromatic Al Kα radiation, with binding energies corrected using the C 1 s peak at 284.8 eV as a reference. The soft X-ray absorption spectroscopy (sXAS) spectra were measured at station BL10B of the National Synchrotron Radiation Laboratory (NSRL, Hefei, China). Subsequent data reduction, analysis and EXAFS fitting were performed with the Athena and Artemis software packages. Defects in catalysts were determined using electron paramagnetic resonance (EPR, MEX-nano, Bruker, German). Thermal gravimetric analysis (TGA) of the catalyst was conducted on a HS-TGA-101 Thermogravimetric Analyzer. Fourier-transform infrared (FTIR) spectroscopy on the catalyst was performed on a FOLI10-R Fourier-transform infrared spectrometer.

FTIR of pyridine adsorption was recorded on the FOLI10-R Fourier-transform infrared spectrometer (INSA OPTICS) with an in-situ cell and MCT detector. First, mix 5 milligrams of the catalyst with 100 milligrams of KBr thoroughly, and then press them into granules. The sample was in situ reduced at a H₂ (10%H₂/Ar mixed gas) atmosphere at 350 °C for 30 minutes, and then heated at 400 °C for 30 min under vacuum in order to remove the physically adsorbed water. After cooling to 100 °C, a background scan was performed. Pyridine vapor was then introduced into the cell at room temperature for 20 min. Subsequent evacuation was performed at 100 °C for 30 min followed by spectral acquisitions. The spectra presented were obtained by subtracting the spectra recorded before and after pyridine adsorption.

In-situ FTIR measurements of methyl benzoate adsorption were collected with the FOLI10-R Fourier-transform infrared spectrometer with an in-situ cell and MCT detector. Firstly, the catalysts were pre-treated in the in-situ cell in a H₂ (10%H₂-Ar mixed gas) atmosphere at 350 °C for 30 min and then switched to an Ar atmosphere for 30 min to eliminate surface adsorbed substances. Then the background scan of the sample was performed. Methyl benzoate was bubbled into the in situ cell under Ar atmosphere for 40 min. Next, the cell was purged with Ar at 35 °C for 30 min, and the adsorption spectra of methyl benzoate were recorded. Finally, the temperature was increased to 300 °C, and the adsorption spectra of methyl benzoate were recorded at increasing temperature. The in-situ reaction was conducted following the same procedure with H₂ (10%H₂-Ar mixed gas) introduced during the heating process.

Overlayer formation of the catalysts was investigated using hydrogen temperature-programmed reduction (H₂-TPR) on VDsorb-92i. 50 mg of catalyst was treated at 350 ^oC for 30 min under flowing Ar at 30 sccm. After cooling to room temperature, the catalyst was exposed to 10%H₂/Ar (30 sccm) and heated to 800 ^oC at a ramp rate of 10 ^oC/min to determine the reducibility of the catalysts.

The absorption and desorption of H₂ and ethyl p-methylbenzoate on the catalysts were investigated using temperature-programmed desorption (TPD) on VDsorb-92i. 50 mg of catalyst was loaded into a quartz U-reactor and pre-treated at 350 ^oC for 30 min in a flowing 10%H₂/Ar (30 sccm) to simulate the in situ reduction process. After cooling to room temperature, the catalyst was heated to 300 ^oC for 30 min under flowing Ar at 30 sccm to eliminate surface adsorbed substances. After the temperature dropped to 30 °C, the H₂ or ethyl p-methylbenzoate was bubbled onto the catalysts for 40 min under a flow of Ar. The sample was then purged by Ar for 40 min to remove the physically adsorbed substances, and the temperature was heated to 800 °C at a heating rate of 10 °C·min⁻¹.

Author contributions

Y.J. and X.C. conceived and supervised the project. Y.J. and Y.L. designed the experiments. Y.L., W.N., K.Z., H.R. and P.Z. conducted the experiments and analyzed the data. Y.L. wrote the paper. Y.J., X.C. and Y.L. revised the manuscript. All authors participated in discussions.

Peer review

Peer review information

Nature Communications thanks Yueqiang Cao, Maria A. Golubeva, and the other anonymous reviewer(s) for their contribution to the peer review of this work. A peer review file is available.

Data availability

Relevant data supporting the key findings of this study are available within the article and the Supplementary Information file. All raw data generated during the current study are available from the corresponding authors upon request. Source data are provided in this paper.

Competing interests

The authors declare no competing interests.

Supplementary information

The online version contains supplementary material available at 10.1038/s41467-026-70743-2.