Light‐Promoted Efficient Gold Recovery Enabled by a Polydopamine‐Functionalized Covalent Organic Framework

ABSTRACT

The rapid proliferation of artificial intelligence (AI) and information technologies is driving a sharp increase in global electronic waste, creating an urgent demand for recovering precious metals like gold from secondary resources to achieve environmental and economic benefits. Herein, a polydopamine (PDA)‐functionalized β‐ketoenamine‐linked covalent organic framework composite, denoted as TATP/PDA, is designed in combination with a light‐assisted strategy for efficient gold recovery. Benefiting from the synergistic effects of hydrogen bonding and π‐π interactions between PDA and the TATP COF, which enhance photoelectric activity and provide abundant adsorption sites, the TATP/PDA exhibits an exceptional adsorption capacity of 5220 mg·g⁻¹, ultrafast adsorption kinetics (>99% removal efficiency within 30 s), and remarkable selectivity in complex matrices. Experimental characterizations disclose that the engineered abundant nitrogen and oxygen active sites, along with the inherent photocatalytic reduction capability, significantly enhance the gold adsorption performance. These key merits position TATP/PDA as one of the best‐performing materials in terms of overall performance. In practical application, TATP/PDA exhibits exceptional performance in recovering gold from real e‐waste leachate. Moreover, the recovered gold‐loaded composite serves as a sustainable photocatalyst for hydrogen evolution. This dual‐benefit strategy not only promotes resource recycling but also contributes to the goals of a green and circular economy.

Bio‐inspired multifunctional polydopamine was strategically integrated into the robust porous TATP framework to create a photoactive TATP/polydopamine adsorbent for efficient gold recovery from e‐waste. The integration of multiple adsorption sites and light‐assisted enhancement synergistically improved the gold recovery performance, while enabling its use as a green photocatalyst for hydrogen evolution.

1. Introduction

With the rapid advancement of artificial intelligence (AI), the demand for computing power has surged exponentially, which in turn accelerates hardware innovation and product replacement cycles. This development leads to mounting electronic waste (e‐waste), which is projected to reach 74.7 million tons annually by 2030 with only 22.3% being recycled [1, 2, 3]. Moreover, this rapidly expanding stream of e‐waste contains valuable precious metals. Particularly, gold plays an indispensable role in electronics on account of its exceptional electrical conductivity, remarkable ductility, and superior chemical stability [4, 5, 6]. Given the scarcity and non‐renewable nature of gold in natural ores, it is imperative to develop efficient and environmentally friendly techniques for recycling gold from secondary resources in terms of fostering a circular economy and ensuring the sustainability of natural resources [7, 8, 9].

Adsorption has emerged as a prominent method for gold recovery because of its operational simplicity, reusability, and cost‐effectiveness [10, 11]. Among available adsorbents, covalent organic frameworks (COFs) stand out on account of their high porosity and stability, tailorable functionality, and metal‐free composition [12]. However, the performance of most COF‐based adsorbents is often limited by the scarcity of active sites on their pore walls, which severely hinders efficient gold recovery [13, 14, 15]. Conventional strategies for functionalizing COFs, either via bottom‐up synthesis or postsynthetic modification, face inherent limitations: the former suffers from limited monomer diversity and stringent crystallization conditions, while the latter is plagued by low efficiency, relatively harsh modification conditions, and unsatisfying reaction universality [16]. Recently, a promising alternative has emerged through the strategic incorporation of functional polymers into porous frameworks [17, 18]. This host‐guest strategy incorporating tailored binding sites is thus expected to serve as a versatile approach for yielding functional COF‐based composites that outperform their pristine individual components [19, 20].

Herein, polydopamine (PDA), a nature mussel‐inspired strong adhesive polymer, was rationally incorporated into the porous frameworks of a β‐ketoenamine‐linked COF (denoted as TATP), synthesized from 4,4',4''‐(1,3,5‐triazine‐2,4,6‐triyl) trianiline (TA) and 1,3,5‐triformylphloroglucinol (TP) to construct the TATP/PDA composite (Scheme 1). The TATP was carefully selected because of its exceptional chemical stability and intrinsic donor‐acceptor (D‐A) system [21, 22, 23, 24]. Meanwhile, PDA was deliberately chosen as a multifunctional guest for its abundant functional groups, contribution to porous structural stabilization, and extensive π‐conjugated electron system [25, 26, 27, 28]. Consequently, the combination of D‐A type COF with photoactive PDA endows the composite with a synergistic enhancement of gold recovery under illumination. The structural and photophysical characterization revealed that the designed TATP/PDA is highly capable of reducing Au(III) into Au(0) under light irradiation. With visible‐light illumination, the TATP/PDA delivered a remarkable gold adsorption capacity of 5220 mg·g⁻¹, ultrafast adsorption kinetics (>99% removal within 30 s using 15 mg adsorbent for 40 mL of 50 ppm Au(III) solution) and excellent recyclability (>99% removal efficiency retained after ten cycles). Furthermore, TATP/PDA efficiently extracted gold from e‐waste with excellent selectivity in practical applications. Importantly, the adsorbed gold was not the final product; the resulting TATP/PDA‐Au served directly as a highly effective photocatalyst for the hydrogen evolution reaction (HER), creating a valuable resource from e‐waste. This work presents a rational strategy for designing high‐performance COF‐based composites that enable efficient gold recovery and subsequent photocatalytic applications, highlighting their dual role in advancing the circular economy and clean energy research.

SCHEME 1.

Schematic illustration of the preparation of TATP/PDA.

2. Results and Discussion

2.1. Synthesis and Characterization

As schematically depicted in Scheme 1, TATP COF was synthesized via a solvothermal reaction using TP and TA as monomers. High crystallinity in the β‐ketoenamine‐linked TATP was achieved by employing pyrrolidine (Py) as a catalyst to facilitate structural rearrangement and by adding NaCl to induce a salting‐out effect, thereby modulating the polymerization kinetics (Figure S1) [29, 30]. Following a mild in‐ situ oxidative polymerization, the resulting TATP/PDA composite exhibited a distinct color change from orange to dark brown, indirectly indicating the successful formation of the composite (Figure 1d,e).

FIGURE 1.

Characterizations of TATP and TATP/PDA. (a) PXRD patterns of TATP with Pawley refinement. (b) PXRD patterns of TATP and TATP/PDA. (c) FT‐IR spectra of PDA, TATP, and TATP/PDA. SEM images of (d) TATP and (e) TATP/PDA (insets: photos of real powder samples). (f) TEM image of TATP/PDA. (g) Nitrogen adsorption‐desorption isotherms of TATP and TATP/PDA measured at 77 K. High‐resolution XPS spectra of (h) N 1s and (i) O 1s for TATP and TATP/PDA.

The powder X‐ray diffraction (PXRD) pattern of TATP (Figure 1a) showed several strong characteristic diffraction peaks consistent with the simulated AA‐stacking model (Figure S2). Pawley refinement was performed to give a hexagonal space group P‐6 with the refinement parameters of R_p = 4.61% and R_wp = 6.62% (Figure 1a and Table S1). Additionally, the PXRD pattern of TATP/PDA closely resembled that of the pristine COF (Figure 1b), demonstrating that the crystalline structure was well preserved after mild polymer incorporation.

Fourier transform infrared (FT‐IR) spectrum of TATP (Figure S3) displayed characteristic peaks at 1626 cm⁻¹, 1579 cm⁻¹ and 1289 cm⁻¹, which can be assigned to C═O, C═C, and C─N bonds, respectively. These features collectively confirm the formation of the β‐ketoenamine linkage [24, 31]. After modification with PDA, the characteristic peak at 3408 cm⁻¹ broadened and redshifted to 3374 cm⁻¹ (Figure 1c), which is attributed to the formation of hydrogen bonding within the composite [32].

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of TATP displayed a uniform nanowire morphology (Figures 1d and S4). The TATP/PDA retained a similar microstructure but displayed denser packing with linear alignment and lamellar stacking, implying strong interactions between TATP and PDA (Figures 1e,f and S5). The Brunauer‐Emmett‐Teller (BET) surface area of the TATP was calculated to be 1172 m²·g⁻¹, determined by nitrogen adsorption‐desorption measurement at 77 K (Figure 1g). Clearly, the observed decrease in surface area and pore volume with increasing PDA content in TATP/PDAs (Figure S7, S8) arose from the adhesion of PDA throughout the porous framework.

The full X‐ray photoelectron spectroscopy (XPS) survey (Figure S9a) and the corresponding high‐resolution XPS spectra (C 1s: Figures S9b and N 1s: 1h, O 1s: 1i) confirmed the formation of the keto‐amine form in the chemical structures of TATP [33]. Specifically, successful PDA incorporation was directly evidenced in the C 1s and N 1s XPS spectra of the composite by the appearance of new peaks at 285.9 eV (C─O) and 401.1 eV (─NH₂), respectively [32, 34]. Comparative XPS analysis revealed discernible shifts in the O 1s and N 1s binding energies of TATP/PDA compared to the pristine TATP (Figure 1h,i), indicative of PDA integration and associated hydrogen bonding [35]. These findings comprehensively demonstrate that the strongly adhesive PDA polymer chains successfully attached to the porous TATP framework.

Then, the chemical and thermal stabilities of the composite were investigated. After being immersed in various solvents (water, hydrochloric acid (pH 1), sodium hydroxide (pH 10), tetrahydrofuran (THF), and dichloromethane (DCM)) for three days, TATP/PDA maintained its well‐defined PXRD patterns and FT‐IR spectra (Figure S10), and no leaching species were detected in the ¹H NMR spectrum (Figure S26), indicative of excellent long‐term chemical stability. Additionally, thermogravimetric analysis (TGA) also indicated that TATP/PDA was thermally stable up to 200°C (Figure S11), reflecting its high thermal stability. These favorable chemical and thermal stabilities underscore the robustness of TATP/PDA, highlighting its suitability for applications in harsh real‐world environments.

2.2. Photophysical and Electrochemical Properties

To further analyze the band structure and charge separation efficiency of the hybridized materials, the samples were systematically investigated by spectroscopic techniques. The ultraviolet‐visible diffuse reflectance spectra (UV‐Vis DRS) of TATP and TATP/PDA exhibited broad absorption across both ultraviolet and visible ranges, with absorption edges at 553 nm and 581 nm, respectively (Figure 2a). The observed red shift upon PDA integration could be attributed to efficient intramolecular charge transfer within the highly conjugated network and strong π‐π stacking interactions [24]. Afterwards, the optical bandgap (E _g) energies, derived from the Kubelka‐Munk transformed spectra, were calculated to be 2.40 eV for TATP and 2.28 eV for TATP/PDA (Figure S12). The positive slopes of the Mott‐Schottky plots confirmed the n‐type semiconductor behavior of both materials, with flat band (FB) potentials of ‐0.87 V and ‐0.58 V (vs. Ag/AgCl), respectively (Figure S13) [36]. Given that the conduction band (CB) potential of n‐type semiconductors lies 0.2 V more negative than the FB value [37], the CB potentials of TATP and TATP/PDA were calculated to be ‐0.87 and ‐0.58 V (vs. NHE), respectively. By combining the E_g and E_CB values, the valence band (VB) positions of the TATP and TATP/PDA were determined to be 1.53 and 1.70 eV (vs. NHE), respectively. As depicted in Figure 2b, the derived energy band structure demonstrated that the CB potential of TATP/PDA was substantially more negative than the standard reduction potential of [AuCl₄]⁻, confirming the thermodynamic feasibility to effectively drive gold ion reduction [38].

FIGURE 2.

Optoelectronic properties of TATP and TATP/PDA. (a) UV‐Vis DRS spectra of TATP and TATP/PDA. (b) Schematic illustration of the electronic band structures of TATP and TATP/PDA. (c) PL spectra of TATP and TATP/PDA. (d) Photocurrent response curves of TATP, TATP/PDA, and TATP/PDA‐Au with the light on/off cycles. (e) Nyquist plots of TATP, TATP/PDA, and TATP/PDA‐Au. (f) EPR conduction band electron spectra of TATP/PDA under dark and light irradiation conditions.

The promising thermodynamic properties of the TATP/PDA prompted an in‐depth investigation of its photoelectric performance. The dramatic photoluminescence (PL) intensity quenching of the composite (Figure 2c) indicated enhanced photoinduced electron transfer between the excited state of the TATP and PDA, thus effectively suppressing photoexcited carrier recombination [28, 39]. Time‐resolved fluorescence (TRFL) decay spectrum of the TATP/PDA showed a decreased fluorescence lifetime, owing to efficient charge carrier migration between TATP and PDA (Figure S14) [40, 41]. Collectively, the quenched PL intensity and shortened lifetime demonstrate excellent carrier extraction capability of TATP/PDA compared to the pristine COF [42]. Furthermore, the composite exhibited a stronger photocurrent response than the pristine TATP under alternating light on/off conditions (Figure 2d). Electrochemical impedance spectroscopy (EIS) revealed a marginally smaller arc radius in the Nyquist plot for the composite (Figure 2e), signifying reduced charge transfer resistance and enhanced carrier transfer efficiency [37]. Compared to dark conditions, the enhanced electron spin resonance spectroscopy (EPR) signal of TATP/PDA under light excitation confirmed an increased generation of photogenerated electrons, thus facilitating the reduction of gold species (Figure 2f) [43]. Owing to its superior photoelectric activity and suitable energy band structure, the proposed TATP/PDA exhibits significant potential for photo‐driven gold recovery.

2.3. Gold Adsorption Study

In view of the successful synthesis of TATP/PDA and its excellent photoelectric activity, a series of photo‐enhanced gold recovery experiments were performed under Xe light irradiation with dark conditions as control. The gold adsorption capacity exhibited a volcanic trend with polymer loading, peaking at 28.95 wt% PDA (Figure S15 and Table S2). The subsequent decline is attributed to pore blockage induced by excess polymer, which reduces the specific surface area and limits the effective exposure of adsorption sites, thereby highlighting the importance of balancing specific surface area and active‐site density through optimization of the PDA content [44, 45]. Maximum gold recovery was achieved at 1% (v/v) methanol concentration, demonstrating the optimal scavenger dosage (Figure S28).

Adsorption isotherms were measured to evaluate adsorption capacities under both dark and light irradiation conditions following a predetermined 12 h equilibrium time (Figure S16). Under light irradiation, TATP/PDA exhibited a maximum gold adsorption capacity of 5220 mg·g⁻¹, representing a 4.1‐fold enhancement over its dark condition capacity (1250 mg·g⁻¹). This capacity significantly surpasses that of pure PDA (3644 mg·g⁻¹ under light; Figure S25), pristine TATP (707 mg·g⁻¹ in dark, 3440 mg·g⁻¹ under light; Figure 3a) and most reported porous materials (Table S3). Notably, the composite exhibited a 1.7‐fold increase in gold adsorption capacity over the pristine COF under dark conditions, an enhancement that further increased to 4.1‐fold under light irradiation. Clearly, the synergy between TATP and PDA critically contributes to the efficient gold recovery by combining abundant redox‐active moieties and superior photoelectric activity. Furthermore, the adsorption performance of TATP/PDA under light irradiation matched well with the Langmuir model with a correlation coefficient of 0.994 and K _L of 0.024 L·mg⁻¹ (Figure S17 and Table S4), revealing the dominant monolayer adsorption of Au(III) on the adsorbent [46].

FIGURE 3.

Gold recovery performance. (a) Adsorption isotherms of TATP and TATP/PDA for Au(III) under dark and light irradiation conditions. (b) Adsorption kinetics performance with the initial concentration of 1000 ppm Au(III). (c) Extraction speed at 50 ppm Au(III) solution. (d) Recovery efficiency of TATP/PDA under different pH values. (e) Zeta potential of TATP/PDA under different pH values. (f) Recovery efficiency of TATP/PDA for different metal ions with multiple competing ions under light irradiation conditions. (g) Distribution factor (K _d) and separation factor (S _q) of TATP/PDA. (h) Gold recovery efficiency of TATP/PDA for ten adsorption cycles. (i) PXRD pattern of TATP/PDA after gold adsorption using 30 mg of adsorbent in 60 mL of 100 ppm Au(III) aqueous solution.

The adsorption kinetics of Au(III) on TATP/PDA were investigated by fitting the time‐dependent adsorption data with the pseudo‐first‐order and pseudo‐second‐order models (Figures 3b and S18). The fitting results (Table S5) revealed that the pseudo‐second‐order model provided a higher correlation coefficient (R² = 0.99), indicating the chemisorption behavior [35]. Further, the extraction speed was tested at a lower concentration (50 ppm) to simulate practical conditions. Notably, TATP/PDA achieved over 99% recovery efficiency within 30 s under light conditions, whereas the same recovery efficiency required 5 min for the composite and 30 min for the pristine COF under dark conditions (Figure 3c). Moreover, treating 100 mL of a ∼1 ppm Au(III) solution with 50 mg of TATP/PDA reduced the residual Au(III) concentration to below 0.5 ppb, as determined by inductively coupled plasma mass spectrometry (ICP‐MS), corresponding to an adsorption efficiency of 99.9% within 30 s (Figure S29). Evidently, TATP/PDA simultaneously delivers ultrahigh adsorption capacity and ultrafast kinetics, which is attributed to the synergy between its readily accessible binding sites and exceptional photoelectric properties.

Considering that pH influences the valence of metal ions and the surface charge of adsorbents, gold recovery efficiency was evaluated across varying pH conditions [15]. As displayed in Figure 3d, over 99% Au(III) was extracted across a broad pH range (1‐10), whereas adsorption efficiency dropped sharply to 1% at pH > 11. Zeta potential analysis was employed to elucidate the electrostatic interactions between adsorbents and gold species. For TATP/PDA, the zeta potential shifted from positive to negative as the pH increased, with an isoelectric point at pH 4.9 (Figure 3e). Under acidic conditions, its positively charged surface effectively adsorbs the anionic [AuCl₄]⁻ species via electrostatic interaction. In contrast, the formation of gold hydroxo species and their strongly negative charge inevitably weakened this interaction under the highly alkaline conditions (pH > 10) [38]. These findings demonstrate that the composite's excellent recovery rate is attributed to electrostatic interactions, particularly in acidic conditions.

For practical applications, the efficient gold recovery under complex conditions is highly desirable. A simulated e‐waste solution containing 5 ppm Au(III) and ∼100 ppm of potential competitive ions (Na⁺, K⁺, Mg²⁺, Ni²⁺, Cu²⁺, Pb²⁺, Zn²⁺, Al³⁺; added as chloride salts) was used to assess the selectivity of TATP/PDA under light irradiation. As displayed in Figure 3f, the composite adsorbed 99.4% of Au(III) with negligible interference from competitive metal ions (only 0.04%–8%). Importantly, the distribution coefficient (K _d) of TATP/PDA for Au(III) reached 8.6×10⁵ mL·g⁻¹, surpassing those of interfering ions by 3–5 orders of magnitude (Figure 3g). This remarkable affinity confirms the superior selectivity toward gold species. The separation factor (S _q), defined as K _dA/K _dB, was used to evaluate the selectivity of TATP/PDA toward different metal ions, where a higher factor value indicates weaker affinity for the competing metal species. The results (Figure 3g) demonstrate exceptional gold separation performance from complex media. The high selectivity of TATP/PDA for Au(III) originates from electrostatic interactions and specific coordination between N/O‐containing functional groups and Au(III) species.

Finally, recyclability was further evaluated considering its crucial role in ensuring long‐term practical application. To evaluate the recyclability of TATP/PDA, the adsorbent was regenerated using thiourea solution. Remarkably, Au(III) recovery efficiency maintained >98% after ten cycles with no significant attenuation (Figure 3h). The composite retained its fiber morphology and chemical structure (Figure S19), confirming its structural stability and enabling sustainable gold recovery from complex matrices. This excellent recyclability is associated with the inherent structural durability of TATP skeleton and the reinforcing hydrogen bonding interactions between the framework and PDA [47]. Thanks to its superior extraction capacity, rapid kinetics, and exceptional recyclability, the proposed TATP/PDA emerges as a highly promising candidate for practical gold recovery applications.

2.4. Adsorption Mechanism

To elucidate the mechanism underlying the excellent gold adsorption performance of TATP/PDA, comprehensive experimental and theoretical analyses were conducted to clarify its interactions with Au(III) species. PXRD analysis revealed the characteristic diffraction peaks of metallic Au(0) (Figure 3i), confirming successful gold capture and reduction mechanism [48]. The resulting gold nanoparticles (∼5‐200 nm) dispersed within the TATP/PDA composite were evidenced by the TEM (Figure 4b), SEM (Figure 4d) and high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) images and corresponding EDX elemental mapping (Figures 4a and S6). Further, high resolution transmission electron microscopy (HRTEM) images resolved a lattice spacing of 2.35 Å, corresponding to the Au (111) plane (Figure 4c). Additionally, ultraviolet‐visible (UV‐Vis) spectra of TATP/PDA in chloroauric acid exhibited a redshifted and broad absorption band, characteristic of the localized surface plasmon resonance (LSPR) of the newly formed gold nanoparticles (Figure S20) [49]. These results demonstrate that Au(III) undergoes reduction followed by adsorption, nucleation, particle migration, and growth into large particles on the TATP/PDA composite, in agreement with classical nucleation theory [50].

FIGURE 4.

Characterizations of TATP/PDA after gold adsorption. (a) HAADF‐STEM and the corresponding EDX elemental maps, (b) TEM, (c) HRTEM, and (d) SEM images of TATP/PDA after gold adsorption. (e) Representative signals of ·O₂ ⁻ in EPR spectra derived from TATP/PDA and TATP/PDA‐Au under different conditions. (f) XPS full spectra of TATP/PDA before and after gold adsorption. (g) Au 4f XPS spectra of TATP/PDA‐Au under dark and light irradiations. (h) O 1s and (i) N 1s XPS spectra of TATP/PDA before and after gold adsorption. (j) Schematic illustration for adsorption mechanism of gold by TATP/PDA.

EPR spectroscopy confirmed the light‐enhanced typical signals of ·O₂ ⁻ generated by TATP/PDA (Figure 4e), indicating its inherent capacity to facilitate electron‐mediated reduction processes, which can be greatly enhanced with light irradiation [51]. In contrast, a markedly weakened ·O₂ ⁻ signal was observed in chloroauric acid solution under light, implying a competitive reaction between Au(III) reduction and ·O₂ ⁻ generation [52]. Furthermore, Au‐loaded TATP/PDA exhibited the highest photocurrent density and lowest charge transfer resistance under illumination (Figure 2d,e), indicating effective charge separation that further facilitates the reduction of gold ions [53].

XPS analysis of TATP/PDA after gold extraction showed distinct Au 4f peaks (Figure 4f), confirming the presence of gold species in the composite. In contrast to the Au(III) precursor observed in the dark, the Au 4f XPS spectrum of TATP/PDA‐Au‐L (“L” means under light irradiation) revealed only Au(I) and Au(0) species (Figure 4g), demonstrating photocatalytic reduction and thereby accounting for the enhanced adsorption capacity [54]. To identify potential binding sites, the high‐resolution O 1s and N 1s XPS spectra of TATP/PDA‐Au‐L were analyzed. After gold extraction, the O 1s XPS spectrum showed a slight shift of the ‐OH peak to higher binding energy alongside a decrease in its area (Figure 4h). These changes indicated that hydroxyl groups complexed with [AuCl₄]⁻ via hydrogen bonding (O─H···Cl) [35] and were simultaneously oxidized to quinones, concomitantly reducing Au(III) to metallic gold [45, 55]. Meanwhile, the N 1s peaks of C═N and C─N shifted to 398.6 and 400.1 eV after gold adsorption (Figure 4i), respectively, implying coordination interactions between gold species and nitrogen‐containing groups. In addition, a new peak emerged at 401.8 eV, assigned to protonated nitrogen species formed in the acidic gold solution. These protonated nitrogenous groups are likely involved in the adsorption and reduction of Au(III) [56]. Complementary electrostatic potential (ESP) maps further provided crucial insights into the electronegativity distribution, with the repeating unit of TATP and dopamine monomer selected as representative structural models (Figure S21). Electron‐rich regions were primarily localized at triazine moieties, carbonyl (C═O) and keto‐amine groups (─NH─) within the TATP skeleton, along with phenolic hydroxyl and amino groups in dopamine. Overall, these electron‐rich structural features critically facilitate gold capture through coordination interactions, thereby significantly increasing accessible binding sites for Au(III).

Building on the solid experimental results, comprehensive characterizations, and theoretical analysis, a sequential mechanism for gold recovery by TATP/PDA is proposed: adsorption, chemical/photo reduction, and nucleation/growth of gold particles on its surface (Figure 4j). Initially, gold species are rapidly captured on the adsorption sites (e.g., electron‐rich N and O) via electrostatic interactions, coordination bonds, and hydrogen bonding [57]. Then, redox‐active groups (e.g., catechol moieties) and nitrogen‐containing groups act as reducing agents to reduce Au(III) to Au(0) through synergistic chemical reduction and photoreduction [15]. Subsequently, the resulting gold clusters continue to crystallize, grow, migrate, and coalesce within the TATP/PDA composite [3, 58]. The synergistic effects of these multiple adsorption mechanisms collectively enable TATP/PDA to achieve exceptional gold recovery efficiency.

2.5. Gold Recovery From the Waste CPU Leachate

For practical demonstration, selective gold recovery from real waste central processing unit (CPU) leachates was evaluated using TATP/PDA. Two end‐of‐life CPUs (AMD and Intel; Figure S22) were disassembled from discarded computers, in which Cu, Ni, and Au elements were predominantly distributed on CPU surfaces as determined by SEM‐EDX mapping (Figure 5a,c). The CPUs were then leached with an aqueous solution of pyridine and N‐bromosuccinimide (NBS) [59]. The resulting blue leachates (Figure S22) were subsequently analyzed by inductively coupled plasma‐optical emission spectrometry (ICP‐OES). The Intel CPU leachate contained 2.7 ppm of Au, 539 ppm of Cu, 756 ppm of Ni, and a trace amount of Zn. Approximately 90% of gold was extracted, whereas only 5.86% of Cu, 1.14% of Ni, and 9.62% of Zn were adsorbed based on initial metal concentrations (Figure 5b). Similarly, the AMD CPU leachate contained 13.5 ppm of Au, 448 ppm of Cu, 490 ppm of Ni and 2.2 ppm of Zn. The composite achieved over 99% gold extraction, compared to only 1.88% Cu, 1.97% Ni, and 4.24% Zn adsorption (Figure 5d). Remarkably, the recovered gold exhibited exceptional purity (>99.3%, 23.8 karat, Figure S22), despite high concentrations of competing ions in leachates. These results clearly confirm the superior gold selectivity of TATP/PDA, validating its potential as a high‐performance adsorbent for practical gold extraction from complex aqueous matrices.

FIGURE 5.

Gold recovery performance of real CPU leachates. SEM images and the corresponding EDX elemental maps of (a) Intel and (c) AMD CPU. Recovery performance of Au(III) in leaching solution of (b) Intel and (d) AMD CPU.

Nowadays, extracting valuable metals from electronic waste offers a straightforward and green route to lowering the cost of metal‐loaded catalysts [38, 60]. Consequently, the gold‐loaded TATP/PDA with minor coadsorption of transition metals recovered from e‐waste was directly employed as a sustainable photocatalyst for the HER. The intrinsic catalytic activity originates from the enhanced photogenerated charge separation of TATP/PDA and the presence of recovered metallic Au(0) species [61, 62].

The SEM images and corresponding EDX element mapping of the recycled adsorbents confirmed homogeneous metal distribution (Figure S23), with corresponding metal loadings quantified by ICP‐OES (Table S6). Under the visible light illumination (λ > 420 nm), photocatalytic hydrogen evolution tests were conducted. The Au‐loaded catalysts, prepared by gold recovery from the Intel and AMD CPU leachates, achieved stable photocatalytic hydrogen evolution rates of 1676 µmol· g⁻¹·h⁻¹ and 1973 µmol· g⁻¹·h⁻¹, respectively (Figure S24). These values represent a substantial enhancement in hydrogen evolution rate over that of pure TATP/PDA (12 µmol· g⁻¹·h⁻¹). This pronounced difference highlights the crucial role of the synergistic effect between the recovered metal species and the TATP/PDA composite in enhancing photocatalytic performance, thus demonstrating the feasibility and versatility of this strategy [9, 38]. Both catalysts maintained their well‐defined PXRD patterns and FT‐IR spectra (Figure S27), indicative of excellent chemical and structural stability.

3. Conclusion

In summary, a TATP/PDA composite is rationally constructed by integration of multifunctional PDA into a highly porous TATP host. Benefiting from its stable porous architecture, exceptional photoelectric properties, and abundant accessible adsorption sites, the designed composite exhibits remarkable gold recovery performance under light irradiation. Notably, it achieves an impressive adsorption capacity of 5220 mg·g⁻¹, which is 4.1‐fold higher than that under dark conditions. The composite also delivers exceptional overall performance, including ultrafast adsorption kinetics (> 99% removal efficiency within 30 s), exceptional selectivity and excellent reusability for gold recovery. Mechanistic studies reveal that synergistic contributions from adsorption, chemical reduction, and photoreduction significantly enhance the overall gold adsorption performance. Leveraging these favorable properties, the composite enables highly selective extraction of trace gold from the real‐world e‐waste leachates. Interestingly, the recovered gold within TATP/PDA subsequently functions as an efficient photocatalyst for hydrogen evolution via water splitting. This work presents an economical and sustainable strategy that harnesses light to boost gold recovery and simultaneously upcycles the captured metal into a value‐added catalyst for clean energy production—offering a promising pathway to advance e‐waste valorization and the circular economy through multifunctional materials design.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting File 1: anie71425‐sup‐0001‐SuppMat.docx.

Data Availability Statement

The data that support the findings of this study are available in the supplementary material of this article.