Highly efficient photosynthesis of syngas and pinacol from CO₂ and 1-phenylethanol via amine-regulated redox pathways

Highly efficient photosynthesis of syngas and pinacol from CO₂ and 1-phenylethanol via amine-regulated redox pathways | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Highly efficient photosynthesis of syngas and pinacol from CO₂ and 1-phenylethanol via amine-regulated redox pathways Wei Lin, Xinyu Xu, Meiyan Guo, Bo Su, Meifang Zheng, Yuanxing FANG, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6624021/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Integrating photocatalytic CO 2 reduction with oxidative organic synthesis offers a promising policy for maximizing charge carrier utilization, enabling the simultaneous production of solar fuels and fine chemicals. Herein, highly efficient photoredox catalysis of CO 2 reduction to syngas (CO: 467.1 μmol·h -1 , H 2 : 78.4 μmol·h -1 ), coupled with 1-phenylethanol oxidation to pinacol (553.9 μmol·h -1 ) is attained over diethylenetriamine modified CdS, delivering a record-high apparent quantum yield of 25%, 100% pinacol selectivity, and a unity reaction stoichiometry. The amine groups effectively modulate both the reductive and oxidative pathways by enhancing CO 2 capture and activation and stabilizing C-centered radicals, respectively. Also, they prompt charge carrier separation and transfer by forming strong Cd-N bonds with CdS. Mechanistic studies reveal that excited holes drive 1-phenylethanol oxidation to pinacol via carbon radical dimerization, while donating protons to boost CO 2 -to-CO reduction via sequential proton-assisted electron transfer processes. This work lights up the route for building advanced artificial photosynthetic systems through precise surface engineering with functional organic groups. Physical sciences/Chemistry/Catalysis/Photocatalysis Physical sciences/Chemistry/Catalysis/Catalytic mechanisms Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Photocatalytic CO 2 reduction by H 2 O presents a sustainable tactic for producing syngas (CO and H 2 ), a highly favorite feedstock in the chemical industry. 1 – 5 However, this strategy confronts challenges due to the extreme stability of CO 2 molecules, fast recombination of photoinduced carriers, and sluggish kinetics of the oxidative half-reaction. 6 – 8 While massive efforts have been made to enhance CO 2 adsorption, activation and photocarrier separation, much less attention has been directed toward hastening the demanding H 2 O oxidation half-reaction, which requires a high overpotential and a complex four-electron/proton transfer to form O 2 . 9 – 12 Moreover, O 2 as a low-value by-product not only complicates syngas utilization before separation but also competes with CO 2 reduction by capturing excited electrons, yielding system-damaging reactive oxygen species. Alternatively, using specific electron donors to replace H 2 O as hole scavengers can reinforce CO 2 conversion, yet this modus operandi wastes the hole energy and generates useless oxidation products. Coupling photocatalytic CO 2 reduction with thermodynamically and kinetically favorable organic oxidation has recently attracted significant interest. 13 – 15 Such redox systems permit the full use of excited electrons and holes, affording valuable reduction and oxidation products concurrently. When properly integrated, the redox reaction can establish a synergistic interplay: protons abstracted from organic dehydrogenation facilitate CO 2 reduction via a proton-coupled fashion, while the swift proton consumption in CO 2 conversion, in turn, drives the oxidative conversion forward. Wu’s group reported CO₂ reduction to CO coupled with 1-phenylethanol dimerization to pinacol—an essential structural motif in pharmaceutical intermediates—achieving a moderate apparent quantum yield (AQY) of 0.9%. 16 Subsequently, efforts to integrate CO 2 conversion to syngas with selective C-N or C-C bond formation emerged, yet the efficiencies remain limited. 17 – 22 Therefore, we are inspired to develop advanced photosynthetic systems with satisfied activity, selectivity, and reaction stoichiometry. Regulating redox pathways by optimizing reactant adsorption, stabilizing intermediates and accelerating product desorption is a powerful approach to improve CO 2 reduction. Similar to noble metals, diethylenetriamine (DETA) anchored on sulfide catalysts can also augment CO 2 adsorption and activation to form the key intermediate COOH* in CO 2 electroreduction. 23 These critical functions of DETA are further validated in our recent works on CO 2 photoreduction to syngas. 24 – 26 As well, DETA tailors the catalyst’s microstructure, imparting preferred surface properties to assist heterogeneous photocatalysis. 27 , 28 By accurately modifying DETA onto suitable catalysts and pairing redox reactions, its merits for CO 2 valorization are expected to be extended and enlarged, enabling efficient synthesis of high-value energetic fuels and fine chemicals. Herein, we demonstrate that DETA anchored on CdS tunes the photoredox pathways of CO 2 reduction and 1-phenylethanol oxidation, achieving excellent yields for syngas (CO: 467.1 µmol·h − 1 , H 2 : 78.4 µmol·h − 1 ) and pinacol (553.9 µmol·h − 1 ), along with superior stability and reusability. Remarkably, this redox system attains a record-high AQY of 25%, a pinacol selectivity of 100%, and an almost unity reaction stoichiometry. Experimental and theoretical results reveal that amine groups strengthen CO 2 adsorption/activation and promote H 2 O desorption to enhance CO 2 reduction; at the same time, they stabilize carbon-centered radicals for C-C coupling, ensuring selective 1-phenylethanol oxidation to pinacol. Besides, the strong Cd-N interactions between CdS and DETA foster charge carrier transfer and impede their recombination, further encouraging the redox reaction. The prime intermediates in CO 2 reduction and key radicals in 1-phenylethanol coupling are identified by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in situ electron paramagnetic resonance (EPR) and corroborated by density functional theory (DFT) calculations. At last, the possible mechanism for the cooperative photoredox cycles is proposed. Results Catalyst Synthesis and Characterizations The CdS-DETA catalysts were prepared via a solvothermal reaction between Cd 2+ and thiourea in a DETA solvent. Bare CdS was obtained by removing the amine groups from CdS-DETA by a hydrothermal treatment. Both CdS-DETA and CdS are indexed to a hexagonal wurtzite structure (JCPDS no.: 41-1049, Fig. S1a). The Fourier transform infrared (FTIR) spectrum of CdS-DETA presents the characteristic signals of -NH 2 , C-H, N-H and C-N species (Fig. 1a), which are not detected on CdS, indicating the removal of DETA. 23,29 CdS-DETA exhibits type-II N 2 adsorption-desorption isotherms with a much higher specific surface area (S BET ) than CdS (Fig. S1b), indicating that DETA modification modulates the textural property. DETA decoration adjusts the morphology and microstructure of CdS. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirm that CdS-DETA adopts an aggregate nanosheet-assembled structure (Fig. 1b, and Fig. S2a), which differs from bare CdS constructed by randomly-connected nanorods (Fig. S3a and b). The expanded aberration-corrected integrated differential phase contrast (AC-iDPC) image gives lattice fringes with a d-spacing of 0.31 nm (Fig. 1c), corresponding to the (101) crystal plane of hexagonal CdS. Elemental mapping confirms the chemical composition (i.e., Cd, S, N and C) and the uniform distribution of DETA on the CdS surface (Fig. 1d). Moreover, electron energy loss spectroscopy (EELS) analysis verifies the presence of N on the CdS surface, highlighting the strong interaction between CdS and DETA groups (Fig. 1e and Fig. S2b). X-ray absorption spectroscopy (XAS) reveals a shift in the Cd K-edge of CdS-DETA toward a higher energy position compared to CdS (Fig. 1f), signifying an increased oxidation state of Cd upon DETA anchoring. 30 This shift suggests an electron transfer from CdS to DETA during CdS-DETA formation. The Fourier-transformed extended X-ray absorption fine structure (FT-EXAFS) spectra exhibit a new peak at 1.25 Å (Fig. 1g), corresponding to Cd-N coordination, which is present in CdS-DETA but absent in bare CdS. Consistently, the wavelet-transformed EXAFS spectrum of CdS-DETA shows a distinct Cd-N coordination peak (Fig. 1h), which is not observed in CdS (Fig. 1i). Moreover, EXAFS fitting analysis confirms that CdS only contains Cd-S coordination with a coordination number of 4.2 and a bond length of 2.52 Å (Table S1). In contrast, CdS-DETA exhibits two coordination environments (i.e., Cd-S and Cd-N) with coordination numbers of 4.1 and 0.3, and bond lengths of 2.50 and 2.01 Å, respectively. These XAS results highlight the strong Cd-N interaction between CdS and DETA, which likely serves as an efficient electron transfer “tunnel” to promote charge migration during photoredox reactions. The CO 2 adsorption measurements show that the CO 2 uptake of CdS-DETA is about twice that of CdS (Fig. S4). Temperature-programmed desorption of CO 2 (CO 2 -TPD) indicates the enhanced CO 2 chemisorption of CdS after DETA modification (Fig. S5). In the CO 2 -TPD profiles, the peak at around 50-150 °C associates with the release of physically adsorbed CO 2 . A distinct desorption peak associated with chemisorbed CO 2 occurs at 200-250 °C, but only in that of CdS-DETA. Such outcomes stress that DETA anchoring intensifies both physical and chemical CO 2 adsorption, mirroring the promise of CdS-DETA for CO 2 conversion reactions. Photocatalytic Performance of CO 2 Reduction Integrated with 1-Phenylethanol Oxidation The catalyst performance was evaluated by the photoredox reaction of CO 2 reduction coupled with 1-phenylethanol oxidation at ambient conditions (Table 1). Bare CdS shows moderate activity, producing CO and H 2 as reduction products, along with 2,3-diphenyl-2,3-butanediol (pinacol) and acetophenone as oxidation products. In contrast, CdS-DETA manifests drastically enhanced performance, generating CO, H 2 and pinacol at rates of 467.1, 78.4 and 553.9 μmol·h -1 (i.e., 93.42, 15.68 and 110.78 mmol·g -1 ·h -1 ), respectively. To the best of our knowledge, this represents a state-of-the-art efficiency for photocatalytic CO 2 reduction integrated with oxidative organic synthesis, producing solar fuels and value-added chemicals together (Table S2). Importantly, the reduction and oxidation products are separated spontaneously into gaseous and liquid phases, simplifying the collection and precluding unwanted interplay of products. Product distribution analysis finds that, compared to CdS, CdS-DETA affords significantly enhanced CO 2 -to-CO conversion and pinacol production, while seriously preventing H 2 evolution. These results reflect that the protons released from 1-phenylethanol coupling are selectively used for CO 2 reduction with high efficiency. This, in turn, strongly boosts 1-phenylethanol oxidation, constructing a cooperative “win-win” manner that efficiently employs both photogenerated electrons and holes. Furthermore, the generation of oxidation and reduction products reveals a positive correlation with the DETA content on CdS (Fig. S6-S9, Table S3-4). These results highlight the vital role of DETA in enhancing synergistic CO 2 reduction and 1-phenylethanol oxidation. Gas chromatography-mass spectrometry (GC-MS) confirms the non-formation of acetophenone (Fig. S10), which however usually generates during catalytic 1-phenylethanol oxidation, 16,31 revealing the high selectivity of CdS-DETA toward pinacol synthesis. Additionally, no pinacol is produced when using an equal amount of acetophenone to replace 1-phenylethanol, revealing that acetophenone does not serve as an intermediate in the oxidative reaction. Noteworthily, the ratio of syngas to pinacol approaches unity, suggesting the superior stoichiometry of the photoredox reaction that totally engages photoexcited electrons and holes to correspondingly catalyze CO 2 reduction and 1-phenylethanol oxidation. Control experiments demonstrate that the redox system is entirely inactive without the catalyst or in the dark (column 1-3, Fig. 2a), which implies that the reaction proceeds photo-catalytically via light excitation of CdS-DETA. Also, no CO is produced once 1-phenylethanol is removed (column 4), revealing the vital role of oxidative half-reaction in promoting CO 2 reduction by consuming holes. When using triethanolamine (TEOA) as an alternative hole scavenger (column 5), the CO/H 2 yield declines evidently, unveiling the crucial synergy between 1-phenylethanol oxidation and CO 2 reduction in achieving exceptional efficiency. Moreover, in a pure Ar atmosphere (column 6), pinacol production reduces distinctly, further exhibiting interdependence of oxidative and reductive processes. The absence of CO formation in Ar, together with the exclusive generation of 13 CO ( m/z =29) in a 13 CO 2 environment (Fig. 2b), validates that the CO product derives solely from CO 2 gas. The AQY for CO/H 2 production over CdS-DETA is intimately dependent on the wavelength of incident light (Fig. 2c), agreeing well with the UV-vis diffuse reflection spectrum (DRS). This points to the fact that the redox reaction is triggered by photoexcitation of CdS-DETA. Of note, a striking AQY of 25.0% is achieved at 395 nm, which marks a record value for solar-driven CO 2 reduction paired with organic synthesis (Table S2). The product yield trend over time reveals that CO 2 reduction attains high efficiency in the first hour, followed by a gradual decline in the CO/H 2 evolution rate (Fig. 2d). This decrease is mainly attributed to the progressive expenditure of 1-phenylethanol (Fig. 2e), which slows the oxidation half-reaction, thereby weakening proton supply and hole-scavenging efficiency. After a 7-hour reaction, 1-phenylethanol conversion reaches about 81.1%, matching well with pinacol production (1720.0 μmol), ensuring nearly 100% carbon balance. Stability tests reveal that CdS-DETA maintains its activity over six consecutive cycles (Fig. 2f), with virtually unchanged reaction stoichiometry in each cycle. In sharp contrast, pure CdS loses almost all activity after the fourth cycle (Fig. S11). Such results prove that DETA decoration enhances the photochemical stability of CdS. Besides, XRD, FTIR and SEM analyses of the used CdS-DETA sample expose no noticeable changes in the crystal, chemical and morphological structures (Fig. S12), confirming its structural robustness. These findings emphasize the high stability and excellent reusability of CdS-DETA for the cooperative photoredox reaction. Charge-Carrier Dynamics and Band Structure of Catalysts To elucidate the high activity of CdS-DETA, various spectroscopic and electrochemical analyses were performed. Steady-state photo-luminescence (PL) exposes that CdS-DETA manifests evidently declined PL emission compared to CdS (Fig. 3a), revealing the suppressed recombination of electron-hole pairs upon DETA modification. 32,33 In the electrochemical impedance spectra (EIS), the Nyquist plot of CdS-DETA shows a smaller high-frequency semicircle than that of CdS (Fig. 3b), signifying reduced electronic resistance and enhanced charge transport. 34,35 Consistently, CdS-DETA delivers a much higher photocurrent density than pristine CdS (Fig. 3c). 36,37 Femtosecond transient absorption spectroscopy (fs-TAS) was employed to further explore photocarrier dynamics (Fig. S13). The kinetic decay time of CdS-DETA (0.12 ps, Fig. 3d) is markedly shorter than that of CdS (13.77 ps, Fig. 3e), reflecting greatly accelerated charge transfer upon DETA anchoring. 38,39 The linear sweep voltammetry (LSV) curves display the lower onset potential and higher current density of CdS-DETA relative to CdS (Fig. 3f), suggesting the intensified CO 2 activation driven by DETA. 40 These spectroscopic and electrochemical results collectively underline that DETA functionalization hinders charge recombination, boosts charge migration, and strengthens CO 2 activation, thus reinforcing the reaction efficiency. The DRS spectra and the corresponding Tauc plots determine the band gap energies of CdS-DETA (2.62 eV) and CdS (2.35 eV) (Fig. S14). Mott-Schottky plots were used to estimate their conduction band (CB) positions, revealing flat-band potentials of -1.06 V and -0.82 V (vs. normal hydrogen electrode, NHE, pH = 7.0) for CdS-DETA and CdS, respectively (Fig. S15). These values approximate their CB positions, allowing the calculation of their valence band (VB) positions: +1.56 V for CdS-DETA and +1.53 V for CdS. The band structures of CdS-DETA and CdS are schematically illustrated (Fig. S16). Cyclic voltammetry (CV) indicates that the potential of 1-phenylethanol oxidation is about +1.51 V (vs. NHE, pH = 7.0, Fig. S17). While both CdS-DETA and CdS hold suitable potentials for 1-phenylethanol oxidation, CdS-DETA exhibits a larger driving force, which contributes to its better oxidation performance. Photovatalytic Mechanism of CO 2 Reduction Coupled with 1-Phenylethanol Oxidation In situ DRIFTS was used to exploit the main intermediates in CO 2 conversion (Fig. 3g). Under dark conditions, the DRIFTS spectra present distinct signals ascribed to protonated ammonium ion (-NH 3 + ) at 1488 and 1634 cm -1 , as well as carbamate anion (-NH-COO - ), characterized by the skeletal vibrations (1328 cm - 1 ), asymmetric and symmetric -COO - stretches (1373, 1446, and 1557 cm -1 ), N-H deformation (1543 cm -1 ), and C=O stretching (1685 cm -1 ). 41,42 These spectral features indicate efficient CO 2 chemisorption on CdS-DETA, likely occurring via chemisorption-mediated carbamation of adject primary amines with CO 2 . 43-45 Upon light irradiation, a new signal emerges at 1715 cm -1 , corresponding to activated CO 2 molecules (*CO 2 ). 46 Particularly, the formation of *COOH, a crucial intermediate in CO 2 -to-CO conversion via *CO 2 protonation, is confirmed by its characteristic signals (1223 and 1623 cm -1 ). 47,48 Concurrently, the presence of adsorbed CO (*CO, 2162 cm -1 ) is detected, indicating its generation from *COOH via proton-coupled electron transfers, accompanied by releasing H 2 O. 48 The accumulation of H 2 O is corroborated by progressively intensified -OH vibration signals (2836 and 2893 cm - ¹). Moreover, the emergence and gradual enrichment of -NH 2 signals suggest that DETA promotes CO 2 reduction by enriching and freeing *CO 2 species. 23 In contrast, these key species are scarcely noticed on pristine CdS (Fig. S18), underscoring the markedly strengthened CO 2 activation and conversion delivered by DETA. 49,50 To identify the key radicals in 1-phenylethanol oxidation, in situ EPR tests were carried out using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a radical scavenger. The EPR spectrum obtained under light irradiation in the absence of CO 2 manifests coupling constants (α N = 14.9, α H = 22.1) that align with reported values of the carbon radicals (Fig. 3h). 16 However, these signals are absent under dark conditions, indicating that the oxidative reaction proceeds via a carbon radical-mediated pathway. Furthermore, the liquid chromatography-mass spectrometry (LC-MS) analysis confirms the formation of DMPO-C α radical adduct (Fig. S19), presenting direct evidence for the involvement of the radical intermediate in the oxidation process. DFT calculations were conducted to provide theoretical confirmation for the redox cycles. The CO 2 reduction pathway, mediated by DETA's terminal -NH 2 groups on the CdS(101) surface follows these key steps (Fig. 4a and Fig. S21): (i) exothermic CO 2 chemisorption (*CO 2 , ΔG = -0.22 eV) initiates activation; (ii) proton-coupled electron transfer generates *COOH intermediate (ΔG = 0.50 eV); (iii) C-O bond cleavage via the reverse water gas shift-type mechanism yields *CO and *OH; (iv) *OH protonation releases H 2 O, followed by *CO desorption to produce CO gas. The catalytic cycle culminates in active site regeneration, with a moderate energy barrier of 0.60 eV for CO liberation governing the overall reaction kinetics. The free energy landscape of 1-phenylethanol oxidation consists of the following elementary steps (Fig. 4b): (i, ii) sequential vertical chemisorption of two 1-phenylethanol molecules on CdS (101) with favorable adsorption energies (ΔG = -0.79 and -1.05 eV); (iii, v) deprotonation of the adsorbed molecules to form carbon radicals, requiring activation energies of 0.27 and 0.47 eV; (v) radical coupling to generate surface-bound pinacol (ΔG = 0.19 eV); (vi) endothermic product desorption (ΔG = 0.92 eV), identified as the rate-determining step. Of note, the liberated protons boost CO 2 reduction via proton-assisted electron transfers, closing the catalytic cycle. This mechanistic framework highlights the role of surface-stabilized radical intermediates in controlling the reaction thermodynamics. Moreover, the strong thermodynamic preference of pinacol release over acetophenone desorption (vii, ΔG = 1.25 eV, Fig. 4b) explains the excellent selectivity toward pinacol. In contrast, on bare CdS (Fig. S20), the rate-determining step of CO 2 reduction shifts to H 2 O liberation, requiring a higher energy barrier of 0.8 eV. Meanwhile, the deprotonation of two adsorbed 1-phenylethanol molecules to form carbon radicals for C-C coupling meets much greater energy barriers (1.04 and 0.87 eV), whereas the successive deprotonation of a single 1-phenylethanol molecule for C=O formation proceeds with lower energy barriers (0.58 and -0.34 eV), thus favoring acetophenone production. These findings highlight the effectiveness of DETA decoration in modulating both the reductive and oxidative paths by lowering energy barriers. The process of collaborative photocatalytic CO 2 reduction integrated with 1-phenylethanol oxidation over CdS-DETA is clarified schematically in Fig. 4c. Upon photoexcitation, CdS generates electron-hole pairs in the conduction and valence bands. Excited holes oxidize 1-phenylethanol to pinacol via radical coupling, simultaneously distributing protons for CO 2 reduction. While the electrons reduce CO 2 to CO by sequential proton-coupled electron transfers, along with H 2 O formation. A minor fraction of excited electrons participate in proton reduction, leading to H 2 evolution. The synergistic interplay between these half-reactions ensures complete deployment of photoinduced carriers, and importantly, DETA increases CO 2 activation and stabilizes key intermediates, empowering marvelous performance in the redox process. Discussion In summary, the efficient coupling of CO 2 reduction with 1-phenylethanol dimerization is realized over diethylenetriamine-decorated CdS in one photoredox system, generating syngas and pinacol simultaneously, with a record-high AQY of 25%, 100% pinacol selectivity, and a unity reaction stoichiometry. The outstanding efficiency is driven by the amine groups, which optimize both the reductive and oxidative paths by lowering energy barriers and meanwhile accelerating the migration kinetics of charge carriers. The underlying mechanism toward the synergetically reinforced syngas and pinacol production is elucidated by in situ spectroscopic characterizations and theoretical calculations. This work highlights the importance of delicate surface functionalization with organic moieties to optimize redox reaction routes for the co-production of high-value fuels and chemicals using solar energy. Methods Materials Cadmium nitrate tetrahydrate (Cd(NO 3 ) 2 ·4H 2 O), ethanol (anhydrous, 99.7%), acetonitrile (MeCN) and Thiourea (CH 4 N 2 S) were provided from Sinopharm Chemical Reagent Co., Ltd. Diethylenetriamine (C 4 H 13 N 3 , 99%) and 1-phenylethanol (C 8 H 10 O, 99%) was purchased from Aladdin. Cadmium acetate dihydrate (Cd(Ac) 2 ·2H 2 O) was purchased from Adamas. All the chemicals from commercial sources were used without further purification. Synthesis of CdS-DETA 2.1347 g of Cd(NO 3 ) 2 ·4H 2 O and 2.6338 g of thiourea were added into 50 ml DETA. Then, the mixture solution was stirred at 120°C for 30 min. The product was collected by centrifugation, washed with water and ethanol several times, and finally dried at 70°C. Synthesis of CdS CdS was obtained by hydrothermal treatment on CdS-DETA. Specifically, 50 mg CdS-DETA and 50 ml water were added into a 100 ml of Teflon-lined stainless-steel autoclave. After the reaction at 120°C for 12 h, the precipitation was naturally cooled to room temperature and then washed with water and ethanol several times. Afterward, the product was dried at 70°C. Synthesis of CdS-DETA-x x represents the mole ratio of DETA/(DETA + H 2 O) in the solvent. Taking CdS-DETA-0.8 as an example, 2.1347 g of Cd(NO 3 ) 2 ·4H 2 O and 2.6338 g of thiourea were added into 40 ml of DETA and 10 ml of H2O. Then, the mixture solution was stirred at 120°C for 30 min. The product was collected by centrifugation, washed with water and ethanol several times, and finally dried at 70°C. Photocatalytic CO 2 Reduction In a typical photocatalytic carbon dioxide reduction reaction, 5 mg of photocatalyst, 10 ml of acetonitrile, and 500 µl 1-phenylethanol were added into a gas-closed glass reactor. Then, high-purity CO 2 was introduced into the reactor with a partial pressure of 1 atm. A LED lamp (395 nm, 74 mW·cm - 2 ) was used as the light source. The temperature of the reaction system was controlled at 25°C by cooling water. During the photocatalytic process, the reaction mixture was vigorously stirred by a magnetic stirrer. After each reaction, the generated gas products were analyzed and quantified by an Agilent 8890 GC, and the liquid products were analyzed and quantified by GC-MS and Liquid chromatography (LC). The cycle experiments were conducted by recovering the used catalysts and then re-dispersing them into a fresh solution for cycling tests, it is worth noting that after each cycle, the catalyst is left in the reactor for 10h for recovery Declarations Acknowledgments This work was financially supported by the National Natural Science Foundation of China (22372035 and 22302039) and the 111 Project (D16008). Author contributions S.W. conceived and directed the project. X.X. designed the experiments and analyzed the results. M.G. and W.L. conducted theoretical studies. B.S. and M.Z. gave advice on the experiments. X.F.L., C.F., G.Z. and H.Z. participated in the revision of the paper. X.X., W.L. and S.W. prepared the manuscript. All the authors contributed to the analysis and interpretation of the data and commented on the final draft of the manuscript. Competing interests Authors declare that they have no competing interests. References Wang, W., Zhang, W., Deng, C., Sheng, H. & Zhao, J. 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Colloid Interface Sci. 512 , 77-85 (2018). Liu, P. et al. Synergy between Palladium Single Atoms and Nanoparticles via Hydrogen Spillover for Enhancing CO 2 Photoreduction to CH 4 . Adv. Mater. 34 , 2200057 (2022). Zhang, L.-X., Qi, M.-Y., Tang, Z.-R. & Xu, Y.-J. Heterostructure-Engineered Semiconductor Quantum Dots toward Photocatalyzed-Redox Cooperative Coupling Reaction. Research 6 , 0073 (2023). Wang, Q. et al. Bottom-up Synthesis of Single-Crystalline Poly (Triazine Imide) Nanosheets for Photocatalytic Overall Water Splitting. Angew. Chem. Int. Ed. 62 , e202307930 (2023). Wang, Y.-F., Qi, M.-Y., Conte, M., Tang, Z.-R. & Xu, Y.-J. Bimetallic Single Atom/Nanoparticle Ensemble for Efficient Photochemical Cascade Synthesis of Ethylene from Methane. Angew. Chem. Int. Ed. 63 , e202407791 (2024). Liu, F. et al. Poly(triazine imide) Crystals for Efficient CO 2 Photoreduction: Surface Pyridine Nitrogen Dominates the Performance. ACS. Catal 15 , 1018-1026 (2025). Wang, Y.-F., Qi, M.-Y., Conte, M., Tang, Z.-R. & Xu, Y.-J. New Radical Route and Insight for the Highly Efficient Synthesis of Benzimidazoles Integrated with Hydrogen Evolution. Angew. Chem. Int. Ed. 62 , e202304306 (2023). Zhou, M. et al. Construction of Frustrated Lewis Pairs in Poly(heptazine Imide) Nanosheets via Hydrogen Bonds for Boosting CO 2 Photoreduction. Angew. Chem. Int. Ed. 63 , e202407468 (2024). Li, W. et al. Nitrogen-Bridged S−N−Cu Sites for CO 2 Photoreduction to Ethanol with 99.5 % Selectivity in Pure Water. Angew. Chem. Int. Ed. n/a , e202423859 (2025). Bie, C. et al. A Bifunctional CdS/MoO 2 /MoS 2 Catalyst Enhances Photocatalytic H 2 Evolution and Pyruvic Acid Synthesis. Angew. Chem. Int. Ed. 61 , e202212045 (2022). Zhang, J. et al. Electron transfer kinetics in CdS/Pt heterojunction photocatalyst during water splitting. Chin. J. Catal 43 , 2530-2538 (2022). Su, B. et al. Hydroxyl-Bonded Ru on Metallic TiN Surface Catalyzing CO 2 Reduction with H 2 O by Infrared Light. J. Am. Chem. Soc. 145 , 27415-27423 (2023). Potter, M. E., Cho, K. M., Lee, J. J. & Jones, C. W. Role of Alumina Basicity in CO 2 Uptake in 3-Aminopropylsilyl-Grafted Alumina Adsorbents. ChemSusChem 10 , 2192-2201 (2017). Cho, K. M. et al. Amine-Functionalized Graphene/CdS Composite for Photocatalytic Reduction of CO 2 . ACS. Catal 7 , 7064-7069 (2017). Jakobsen, J. B., Rønne, M. H., Daasbjerg, K. & Skrydstrup, T. Are Amines the Holy Grail for Facilitating CO 2 Reduction? Angew. Chem. Int. Ed. 60 , 9174-9179 (2021). Chen, O. I.-F. et al. Water-Enhanced Direct Air Capture of Carbon Dioxide in Metal–Organic Frameworks. J. Am. Chem. Soc. 146 , 2835-2844 (2024). Seo, H., Rahimi, M. & Hatton, T. A. Electrochemical Carbon Dioxide Capture and Release with a Redox-Active Amine. J. Am. Chem. Soc. 144 , 2164-2170 (2022). Wang, J. et al. Effect of S vacancy in Cu 3 SnS 4 on high selectivity and activity of photocatalytic CO 2 reduction. Appl. Catal. B Environ 297 , 120498 (2021). Li, X. et al. Selective visible-light-driven photocatalytic CO 2 reduction to CH 4 mediated by atomically thin CuIn 5 S 8 layers. Nat. Energy 4 , 690-699 (2019). Qi, Y. et al. Fabrication of Black In 2 O 3 with Dense Oxygen Vacancy through Dual Functional Carbon Doping for Enhancing Photothermal CO 2 Hydrogenation. Adv. Funct. Mater. 31 , 2100908 (2021). Tian, T. et al. CdS/ethylenediamine nanowires 3D photocatalyst with rich sulfur vacancies for efficient syngas production from CO 2 photoreduction. Appl. Catal. B Environ 308 , 121227 (2022). Liu, P. et al. Overturning photoreduction product of CO 2 by defect- and COOH-functionalized multi-wall carbon nanotubes. Appl. Catal. B Environ 320 , 121985 (2023). Table Table 1 is available in the Supplementary Files section Additional Declarations There is NO Competing Interest. Supplementary Files SI.docx Supplement data Table1.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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Lin","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAqUlEQVRIiWNgGAWjYDACdsYGhg82YKYBkVqYGRsYZ6SRpgWIeEjSYnCYue2xTUJdYgN78zYJhpo7xGhhbDfOSWBLbOA5VibBcOwZYS1mhxnbpHN/8CQ2SOSYSTA2HCZSi0WCRGKD/BtStDAkGABt4SFSiz1Qi2RPQoJxG09asUXCMSK0SLa3P5P4kVAn289+eOONDzVEaIEDNhCRQIKGUTAKRsEoGAV4AAD+1jKBbTrqFgAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-5046-4765","institution":"Fuzhou University","correspondingAuthor":true,"prefix":"","firstName":"Wei","middleName":"","lastName":"Lin","suffix":""},{"id":462732600,"identity":"7e088936-d093-47e1-b5e9-e66105a3df1d","order_by":1,"name":"Xinyu Xu","email":"","orcid":"","institution":"Fuzhou University","correspondingAuthor":false,"prefix":"","firstName":"Xinyu","middleName":"","lastName":"Xu","suffix":""},{"id":462732601,"identity":"d4cd3573-035c-4e1a-b661-0fafcb9eb2b2","order_by":2,"name":"Meiyan Guo","email":"","orcid":"","institution":"Fuzhou University","correspondingAuthor":false,"prefix":"","firstName":"Meiyan","middleName":"","lastName":"Guo","suffix":""},{"id":462732602,"identity":"56933990-bc75-488b-bd96-16bc3b8e1cb6","order_by":3,"name":"Bo Su","email":"","orcid":"","institution":"Fuzhou University","correspondingAuthor":false,"prefix":"","firstName":"Bo","middleName":"","lastName":"Su","suffix":""},{"id":462732603,"identity":"1812900f-d0e1-4b15-9390-6deedc4866a7","order_by":4,"name":"Meifang Zheng","email":"","orcid":"https://orcid.org/0000-0002-7316-6971","institution":"Fuzhou University","correspondingAuthor":false,"prefix":"","firstName":"Meifang","middleName":"","lastName":"Zheng","suffix":""},{"id":462732604,"identity":"2b06f594-fd8f-4678-8544-ab411bb77528","order_by":5,"name":"Yuanxing FANG","email":"","orcid":"","institution":"Fuzhou University","correspondingAuthor":false,"prefix":"","firstName":"Yuanxing","middleName":"","lastName":"FANG","suffix":""},{"id":462732605,"identity":"dc9ab1a0-912e-4d55-96da-03ab1d97adcc","order_by":6,"name":"Chengyang Feng","email":"","orcid":"https://orcid.org/0000-0002-7437-1088","institution":"King Abdullah University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Chengyang","middleName":"","lastName":"Feng","suffix":""},{"id":462732606,"identity":"8f0adad0-d8f0-419e-89b3-938388ae4be4","order_by":7,"name":"Guigang Zhang","email":"","orcid":"https://orcid.org/0000-0002-9913-488X","institution":"Fuzhou University","correspondingAuthor":false,"prefix":"","firstName":"Guigang","middleName":"","lastName":"Zhang","suffix":""},{"id":462732607,"identity":"a2b483b3-f832-457e-91d4-cfee7f78cad6","order_by":8,"name":"Huabin Zhang","email":"","orcid":"https://orcid.org/0000-0003-1601-2471","institution":"King Abdullah University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Huabin","middleName":"","lastName":"Zhang","suffix":""},{"id":462732608,"identity":"bbc8aaf2-b09f-455b-9c7d-91dd6f278343","order_by":9,"name":"Sibo Wang","email":"","orcid":"https://orcid.org/0000-0003-2656-9169","institution":"Fuzhou University","correspondingAuthor":false,"prefix":"","firstName":"Sibo","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2025-05-09 01:15:14","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-6624021/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6624021/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":83592653,"identity":"53e0c5d0-2e59-414d-b783-9df7db7410e2","added_by":"auto","created_at":"2025-05-29 06:53:24","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":773686,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStructural analysis of CdS-D catalysts.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e FTIR spectra, \u003cstrong\u003eb\u003c/strong\u003e TEM image, \u003cstrong\u003ec\u003c/strong\u003e AC-iDPC image and \u003cstrong\u003ed\u003c/strong\u003e EDS maps of CdS-DETA. \u003cstrong\u003ee\u003c/strong\u003e EELS spectra with N (K-edge) from CdS-DETA and CdS \u003cstrong\u003ef\u003c/strong\u003e Cd K-edge XANES spectra and \u003cstrong\u003eg\u003c/strong\u003e FT-EXAFS spectra of CdS-DETA and CdS. The wavelet-transformed EXAFS spectra of \u003cstrong\u003eh\u003c/strong\u003e CdS-DETA and \u003cstrong\u003ei\u003c/strong\u003e CdS.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6624021/v1/1a0d5f55584ba75b101bb0fa.png"},{"id":83592635,"identity":"9c9f7785-2e9f-428e-b10b-6cf80b44b634","added_by":"auto","created_at":"2025-05-29 06:53:22","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":280245,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePhotocatalytic performances.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Efficiency of the redox reaction under varied conditions. \u003cstrong\u003eb\u003c/strong\u003e Results of GC-MS analysis on CO generated from the \u003csup\u003e13\u003c/sup\u003eCO\u003csub\u003e2\u003c/sub\u003e isotope experiment. \u003cstrong\u003ec\u003c/strong\u003e Wavelength-dependent AQY and DRS spectrum of CdS-DETA. \u003cstrong\u003ed\u003c/strong\u003e Time-yield plots of CO and H\u003csub\u003e2\u003c/sub\u003e, \u003cstrong\u003ee\u003c/strong\u003e time-dependent variations of 1-phenylethanol and pinacol and the corresponding 1-phenylethanol conversion, and \u003cstrong\u003ef\u003c/strong\u003e stability tests of CdS-DETA.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6624021/v1/d3ad328cad63bdc397c51a9a.png"},{"id":83592640,"identity":"74023832-2628-48d8-8024-34f7a02d4832","added_by":"auto","created_at":"2025-05-29 06:53:22","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":521115,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePhoto-electric and in situ characterizations.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Steady-state PL spectra, \u003cstrong\u003eb\u003c/strong\u003e EIS and \u003cstrong\u003ec\u003c/strong\u003e photocurrent generation of CdS and CdS-DETA. Normalized decay kinetic curves of \u003cstrong\u003ed\u003c/strong\u003e CdS and \u003cstrong\u003ee\u003c/strong\u003e CdS-DETA in acetonitrile with 1-pinacol monitored at 732 nm. \u003cstrong\u003ef\u003c/strong\u003e LSV curves of CdS and CdS-DETA in CO\u003csub\u003e2\u003c/sub\u003e-saturated solution. \u003cstrong\u003eg\u003c/strong\u003e \u003cem\u003eIn situ\u003c/em\u003e DRIFTS spectra of CdS-DETA in a CO\u003csub\u003e2\u003c/sub\u003e-saturated atmosphere with and without light illumination. \u003cstrong\u003eh\u003c/strong\u003e EPR spectra of CdS-DETA in Ar-saturated 1-phenylethanol solution with and without light illumination.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6624021/v1/44d60e69f1f954689f45fcee.png"},{"id":83592668,"identity":"beaa36fd-06cc-49b4-90bb-2388b9cea36d","added_by":"auto","created_at":"2025-05-29 06:53:25","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":402593,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDFT calculations and the proposed reaction mechanism.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Free energy diagram of CO\u003csub\u003e2\u003c/sub\u003e reduction to CO on DETA/CdS (101) surface. The gray, brown, red, white, pink, and yellow atoms represent N, C, O, H, Cd and S atoms, respectively, and * denotes active sites. \u003cstrong\u003eb\u003c/strong\u003e Free energy diagram of 1-phenylethanol oxidation on DETA/CdS (101) surface. \u003cstrong\u003ec\u003c/strong\u003e Schematic illustration of the photocatalytic process of CO\u003csub\u003e2\u003c/sub\u003e reduction and 1-phenylethanol oxidation over CdS-DETA.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6624021/v1/f5715b79ff2bc7b6405f15c5.png"},{"id":88377044,"identity":"0e576635-5d08-4095-91eb-386e927b0aef","added_by":"auto","created_at":"2025-08-05 21:48:32","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2680799,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6624021/v1/3ef9dadd-209c-4890-b102-18a3cd02aa67.pdf"},{"id":83592642,"identity":"6770f1ff-edaa-48d7-9a97-cf799c830446","added_by":"auto","created_at":"2025-05-29 06:53:23","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":3240534,"visible":true,"origin":"","legend":"Supplement data","description":"","filename":"SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-6624021/v1/01c6ef53969015ebac629ee2.docx"},{"id":83592670,"identity":"61b736d3-52b6-44f3-9bf9-da8fba2b1b14","added_by":"auto","created_at":"2025-05-29 06:53:26","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":44811,"visible":true,"origin":"","legend":"","description":"","filename":"Table1.docx","url":"https://assets-eu.researchsquare.com/files/rs-6624021/v1/94d03b93a099e491cfb456e4.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Highly efficient photosynthesis of syngas and pinacol from CO₂ and 1-phenylethanol via amine-regulated redox pathways","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePhotocatalytic CO\u003csub\u003e2\u003c/sub\u003e reduction by H\u003csub\u003e2\u003c/sub\u003eO presents a sustainable tactic for producing syngas (CO and H\u003csub\u003e2\u003c/sub\u003e), a highly favorite feedstock in the chemical industry.\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e However, this strategy confronts challenges due to the extreme stability of CO\u003csub\u003e2\u003c/sub\u003e molecules, fast recombination of photoinduced carriers, and sluggish kinetics of the oxidative half-reaction.\u003csup\u003e\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e While massive efforts have been made to enhance CO\u003csub\u003e2\u003c/sub\u003e adsorption, activation and photocarrier separation, much less attention has been directed toward hastening the demanding H\u003csub\u003e2\u003c/sub\u003eO oxidation half-reaction, which requires a high overpotential and a complex four-electron/proton transfer to form O\u003csub\u003e2\u003c/sub\u003e.\u003csup\u003e\u003cspan additionalcitationids=\"CR10 CR11\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e Moreover, O\u003csub\u003e2\u003c/sub\u003e as a low-value by-product not only complicates syngas utilization before separation but also competes with CO\u003csub\u003e2\u003c/sub\u003e reduction by capturing excited electrons, yielding system-damaging reactive oxygen species. Alternatively, using specific electron donors to replace H\u003csub\u003e2\u003c/sub\u003eO as hole scavengers can reinforce CO\u003csub\u003e2\u003c/sub\u003e conversion, yet this modus operandi wastes the hole energy and generates useless oxidation products.\u003c/p\u003e \u003cp\u003eCoupling photocatalytic CO\u003csub\u003e2\u003c/sub\u003e reduction with thermodynamically and kinetically favorable organic oxidation has recently attracted significant interest.\u003csup\u003e\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e Such redox systems permit the full use of excited electrons and holes, affording valuable reduction and oxidation products concurrently. When properly integrated, the redox reaction can establish a synergistic interplay: protons abstracted from organic dehydrogenation facilitate CO\u003csub\u003e2\u003c/sub\u003e reduction via a proton-coupled fashion, while the swift proton consumption in CO\u003csub\u003e2\u003c/sub\u003e conversion, in turn, drives the oxidative conversion forward. Wu\u0026rsquo;s group reported CO₂ reduction to CO coupled with 1-phenylethanol dimerization to pinacol\u0026mdash;an essential structural motif in pharmaceutical intermediates\u0026mdash;achieving a moderate apparent quantum yield (AQY) of 0.9%.\u003csup\u003e16\u003c/sup\u003e Subsequently, efforts to integrate CO\u003csub\u003e2\u003c/sub\u003e conversion to syngas with selective C-N or C-C bond formation emerged, yet the efficiencies remain limited.\u003csup\u003e\u003cspan additionalcitationids=\"CR18 CR19 CR20 CR21\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e Therefore, we are inspired to develop advanced photosynthetic systems with satisfied activity, selectivity, and reaction stoichiometry.\u003c/p\u003e \u003cp\u003eRegulating redox pathways by optimizing reactant adsorption, stabilizing intermediates and accelerating product desorption is a powerful approach to improve CO\u003csub\u003e2\u003c/sub\u003e reduction. Similar to noble metals, diethylenetriamine (DETA) anchored on sulfide catalysts can also augment CO\u003csub\u003e2\u003c/sub\u003e adsorption and activation to form the key intermediate COOH* in CO\u003csub\u003e2\u003c/sub\u003e electroreduction.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e These critical functions of DETA are further validated in our recent works on CO\u003csub\u003e2\u003c/sub\u003e photoreduction to syngas.\u003csup\u003e\u003cspan additionalcitationids=\"CR25\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e As well, DETA tailors the catalyst\u0026rsquo;s microstructure, imparting preferred surface properties to assist heterogeneous photocatalysis.\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e By accurately modifying DETA onto suitable catalysts and pairing redox reactions, its merits for CO\u003csub\u003e2\u003c/sub\u003e valorization are expected to be extended and enlarged, enabling efficient synthesis of high-value energetic fuels and fine chemicals.\u003c/p\u003e \u003cp\u003eHerein, we demonstrate that DETA anchored on CdS tunes the photoredox pathways of CO\u003csub\u003e2\u003c/sub\u003e reduction and 1-phenylethanol oxidation, achieving excellent yields for syngas (CO: 467.1 \u0026micro;mol\u0026middot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, H\u003csub\u003e2\u003c/sub\u003e: 78.4 \u0026micro;mol\u0026middot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and pinacol (553.9 \u0026micro;mol\u0026middot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), along with superior stability and reusability. Remarkably, this redox system attains a record-high AQY of 25%, a pinacol selectivity of 100%, and an almost unity reaction stoichiometry. Experimental and theoretical results reveal that amine groups strengthen CO\u003csub\u003e2\u003c/sub\u003e adsorption/activation and promote H\u003csub\u003e2\u003c/sub\u003eO desorption to enhance CO\u003csub\u003e2\u003c/sub\u003e reduction; at the same time, they stabilize carbon-centered radicals for C-C coupling, ensuring selective 1-phenylethanol oxidation to pinacol. Besides, the strong Cd-N interactions between CdS and DETA foster charge carrier transfer and impede their recombination, further encouraging the redox reaction. The prime intermediates in CO\u003csub\u003e2\u003c/sub\u003e reduction and key radicals in 1-phenylethanol coupling are identified by \u003cem\u003ein situ\u003c/em\u003e diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and \u003cem\u003ein situ\u003c/em\u003e electron paramagnetic resonance (EPR) and corroborated by density functional theory (DFT) calculations. At last, the possible mechanism for the cooperative photoredox cycles is proposed.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eCatalyst Synthesis and Characterizations\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe CdS-DETA catalysts were prepared via a solvothermal reaction between Cd\u003csup\u003e2+\u003c/sup\u003e and thiourea in a DETA solvent. Bare CdS was obtained by removing the amine groups from CdS-DETA by a hydrothermal treatment. Both CdS-DETA and CdS are indexed to a hexagonal wurtzite structure (JCPDS no.: 41-1049, Fig. S1a). The Fourier transform infrared (FTIR) spectrum of CdS-DETA presents the characteristic signals of -NH\u003csub\u003e2\u003c/sub\u003e, C-H, N-H and C-N species (Fig. 1a), which are not detected on CdS, indicating the removal of DETA.\u003csup\u003e23,29\u003c/sup\u003e CdS-DETA exhibits type-II N\u003csub\u003e2\u003c/sub\u003e adsorption-desorption isotherms with a much higher specific\u0026nbsp;surface area (S\u003csub\u003eBET\u003c/sub\u003e) than CdS (Fig. S1b), indicating that DETA modification modulates the textural property.\u003c/p\u003e\n\u003cp\u003eDETA decoration adjusts the morphology and microstructure of CdS. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirm that CdS-DETA adopts an aggregate nanosheet-assembled structure (Fig. 1b, and Fig. S2a), which differs from bare CdS constructed by randomly-connected nanorods (Fig. S3a and b). The expanded aberration-corrected integrated differential phase contrast (AC-iDPC) image gives lattice fringes with a d-spacing of 0.31 nm (Fig. 1c), corresponding to the (101) crystal plane of hexagonal CdS. Elemental mapping confirms the chemical composition (i.e., Cd, S, N and C) and the uniform distribution of DETA on the CdS surface (Fig. 1d). Moreover, electron energy loss spectroscopy (EELS) analysis verifies the presence of N on the CdS surface, highlighting the strong interaction between CdS and DETA groups (Fig. 1e and Fig. S2b).\u003c/p\u003e\n\u003cp\u003eX-ray absorption spectroscopy (XAS) reveals a shift in the Cd K-edge of CdS-DETA toward a higher energy position compared to CdS (Fig. 1f), signifying an increased oxidation state of Cd upon DETA anchoring.\u003csup\u003e30\u003c/sup\u003e This shift suggests an electron transfer from CdS to DETA during CdS-DETA formation. The Fourier-transformed extended X-ray absorption fine structure (FT-EXAFS) spectra exhibit a new peak at 1.25 \u0026Aring; (Fig. 1g), corresponding to Cd-N coordination, which is present in CdS-DETA but absent in bare CdS. Consistently, the wavelet-transformed EXAFS spectrum of CdS-DETA shows a distinct Cd-N coordination peak (Fig. 1h), which is not observed in CdS (Fig. 1i). Moreover, EXAFS fitting analysis \u0026nbsp; confirms that CdS only contains Cd-S coordination with a coordination number of 4.2 and a bond length of 2.52 \u0026Aring; (Table S1). In contrast, CdS-DETA exhibits two coordination environments (i.e., Cd-S and Cd-N) with coordination numbers of 4.1 and 0.3, and bond lengths of 2.50 and 2.01 \u0026Aring;, respectively. These XAS results highlight the strong Cd-N interaction between CdS and DETA, which likely serves as an efficient electron transfer \u0026ldquo;tunnel\u0026rdquo; to promote charge migration during photoredox reactions.\u003c/p\u003e\n\u003cp\u003eThe CO\u003csub\u003e2\u003c/sub\u003e adsorption measurements show that the CO\u003csub\u003e2\u0026nbsp;\u003c/sub\u003euptake of CdS-DETA is about twice that of CdS (Fig. S4). Temperature-programmed desorption of CO\u003csub\u003e2\u003c/sub\u003e (CO\u003csub\u003e2\u003c/sub\u003e-TPD) indicates the enhanced CO\u003csub\u003e2\u003c/sub\u003e chemisorption of CdS after DETA modification (Fig. S5). In the CO\u003csub\u003e2\u003c/sub\u003e-TPD profiles, the peak at around 50-150 \u0026deg;C associates with the release of physically adsorbed CO\u003csub\u003e2\u003c/sub\u003e. A distinct desorption peak associated with chemisorbed CO\u003csub\u003e2\u003c/sub\u003e occurs at 200-250 \u0026deg;C, but only in that of CdS-DETA. Such outcomes stress that DETA anchoring intensifies both physical and chemical CO\u003csub\u003e2\u003c/sub\u003e adsorption, mirroring the promise of CdS-DETA for CO\u003csub\u003e2\u003c/sub\u003e conversion reactions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhotocatalytic Performance of CO\u003csub\u003e2\u003c/sub\u003e Reduction\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eIntegrated with 1-Phenylethanol Oxidation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe catalyst performance was evaluated by the photoredox reaction of CO\u003csub\u003e2\u003c/sub\u003e reduction coupled with 1-phenylethanol oxidation at ambient conditions (Table 1). Bare CdS shows moderate activity, producing CO and H\u003csub\u003e2\u003c/sub\u003e as reduction products, along with 2,3-diphenyl-2,3-butanediol (pinacol) and acetophenone as oxidation products. In contrast, CdS-DETA manifests drastically enhanced performance, generating CO, H\u003csub\u003e2\u003c/sub\u003e and pinacol at rates of 467.1, 78.4 and 553.9 \u0026mu;mol\u0026middot;h\u003csup\u003e-1\u003c/sup\u003e (i.e., 93.42, 15.68 and 110.78 mmol\u0026middot;g\u003csup\u003e-1\u003c/sup\u003e\u0026middot;h\u003csup\u003e-1\u003c/sup\u003e), respectively. To the best of our knowledge, this represents a state-of-the-art efficiency for photocatalytic CO\u003csub\u003e2\u003c/sub\u003e reduction integrated with oxidative organic synthesis, producing solar fuels and value-added chemicals together (Table S2). Importantly, the reduction and oxidation products are separated spontaneously into gaseous and liquid phases, simplifying the collection and precluding unwanted interplay of products.\u003c/p\u003e\n\u003cp\u003eProduct distribution analysis finds that, compared to CdS, CdS-DETA affords significantly enhanced CO\u003csub\u003e2\u003c/sub\u003e-to-CO conversion and pinacol production, while seriously preventing H\u003csub\u003e2\u003c/sub\u003e evolution. These results reflect that the protons released from 1-phenylethanol coupling are selectively used for CO\u003csub\u003e2\u003c/sub\u003e reduction with high efficiency. This, in turn, strongly boosts 1-phenylethanol oxidation, constructing a cooperative \u0026ldquo;win-win\u0026rdquo; manner that efficiently employs both photogenerated electrons and holes. Furthermore, the generation of oxidation and reduction products reveals a positive correlation with the DETA content on CdS (Fig. S6-S9, Table S3-4). These results highlight the vital role of DETA in enhancing synergistic CO\u003csub\u003e2\u003c/sub\u003e reduction and 1-phenylethanol oxidation.\u003c/p\u003e\n\u003cp\u003eGas chromatography-mass spectrometry (GC-MS) confirms the non-formation of acetophenone (Fig. S10), which however usually generates during catalytic 1-phenylethanol oxidation,\u003csup\u003e16,31\u003c/sup\u003e revealing the high selectivity of CdS-DETA toward pinacol synthesis. Additionally, no pinacol is produced when using an equal amount of acetophenone to replace 1-phenylethanol, revealing that acetophenone does not serve as an intermediate in the oxidative reaction. Noteworthily, the ratio of syngas to pinacol approaches unity, suggesting the superior stoichiometry of the photoredox reaction that totally engages photoexcited electrons and holes to correspondingly catalyze CO\u003csub\u003e2\u003c/sub\u003e reduction and 1-phenylethanol oxidation.\u003c/p\u003e\n\u003cp\u003eControl experiments demonstrate that the redox system is entirely inactive without the catalyst or in the dark (column 1-3, Fig. 2a), which implies that the reaction proceeds photo-catalytically via light excitation of CdS-DETA. Also, no CO is produced once 1-phenylethanol is removed (column 4), revealing the vital role of oxidative half-reaction in promoting CO\u003csub\u003e2\u003c/sub\u003e reduction by consuming holes. When using triethanolamine (TEOA) as an alternative hole scavenger (column 5), the CO/H\u003csub\u003e2\u003c/sub\u003e yield declines evidently, unveiling the crucial synergy between 1-phenylethanol oxidation and CO\u003csub\u003e2\u003c/sub\u003e reduction in achieving exceptional efficiency. Moreover, in a pure Ar atmosphere (column 6), pinacol production reduces distinctly, further exhibiting interdependence of oxidative and reductive processes. The absence of CO formation in Ar, together with the exclusive generation of \u003csup\u003e13\u003c/sup\u003eCO (\u003cem\u003em/z\u003c/em\u003e =29) in a \u003csup\u003e13\u003c/sup\u003eCO\u003csub\u003e2\u003c/sub\u003e environment (Fig. 2b), validates that the CO product derives solely from CO\u003csub\u003e2\u003c/sub\u003e gas.\u003c/p\u003e\n\u003cp\u003eThe AQY for CO/H\u003csub\u003e2\u003c/sub\u003e production over CdS-DETA is intimately dependent on the wavelength of incident light (Fig. 2c), agreeing well with the UV-vis diffuse reflection spectrum (DRS). This points to the fact that the redox reaction is triggered by photoexcitation of CdS-DETA. Of note, a striking AQY of 25.0% is achieved at 395 nm, which marks a record value for solar-driven CO\u003csub\u003e2\u003c/sub\u003e reduction paired with organic synthesis (Table S2).\u003c/p\u003e\n\u003cp\u003eThe product yield trend over time reveals that CO\u003csub\u003e2\u003c/sub\u003e reduction attains high efficiency in the first hour, followed by a gradual decline in the CO/H\u003csub\u003e2\u003c/sub\u003e evolution rate (Fig. 2d). This decrease is mainly attributed to the progressive expenditure of 1-phenylethanol (Fig. 2e), which slows the oxidation half-reaction, thereby weakening proton supply and hole-scavenging efficiency. After a 7-hour reaction, 1-phenylethanol conversion reaches about 81.1%, matching well with pinacol production (1720.0 \u0026mu;mol), ensuring nearly 100% carbon balance.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eStability tests reveal that CdS-DETA maintains its activity over six consecutive cycles (Fig. 2f), with virtually unchanged reaction stoichiometry in each cycle. In sharp contrast, pure CdS loses almost all activity after the fourth cycle (Fig. S11). Such results prove that DETA decoration enhances the photochemical stability of CdS. Besides, XRD, FTIR and SEM analyses of the used CdS-DETA sample expose no noticeable changes in the crystal, chemical and morphological structures (Fig. S12), confirming its structural robustness. These findings emphasize the high stability and excellent reusability of CdS-DETA for the cooperative photoredox reaction.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCharge-Carrier Dynamics and Band Structure of Catalysts\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo elucidate the high activity of CdS-DETA, various spectroscopic and electrochemical analyses were performed. Steady-state photo-luminescence (PL) exposes that CdS-DETA manifests evidently declined PL emission compared to CdS (Fig. 3a), revealing the suppressed recombination of electron-hole pairs upon DETA modification.\u003csup\u003e32,33\u003c/sup\u003e In the electrochemical impedance spectra (EIS), the Nyquist plot of CdS-DETA shows a smaller high-frequency semicircle than that of CdS (Fig. 3b), signifying reduced electronic resistance and enhanced charge transport.\u003csup\u003e34,35\u003c/sup\u003e Consistently, CdS-DETA delivers a much higher photocurrent density than pristine CdS (Fig. 3c).\u003csup\u003e36,37\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eFemtosecond transient absorption spectroscopy (fs-TAS) was employed to further explore photocarrier dynamics (Fig. S13). The kinetic decay time of CdS-DETA (0.12 ps, Fig. 3d) is markedly shorter than that of CdS (13.77 ps, Fig. 3e), reflecting greatly accelerated charge transfer upon DETA anchoring.\u003csup\u003e38,39\u003c/sup\u003e The linear sweep voltammetry (LSV) curves display the lower onset potential and higher current density of CdS-DETA relative to CdS (Fig. 3f), suggesting the intensified CO\u003csub\u003e2\u0026nbsp;\u003c/sub\u003eactivation driven by DETA.\u003csup\u003e40\u003c/sup\u003e These spectroscopic and electrochemical results collectively underline that DETA functionalization hinders charge recombination, boosts charge migration, and strengthens CO\u003csub\u003e2\u003c/sub\u003e activation, thus reinforcing the reaction efficiency.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe DRS spectra and the corresponding Tauc plots determine the band gap energies of CdS-DETA (2.62 eV) and CdS (2.35 eV) (Fig. S14). Mott-Schottky plots were used to estimate their conduction band (CB) positions, revealing flat-band potentials of -1.06 V and -0.82 V (vs. normal hydrogen electrode, NHE, pH = 7.0) for CdS-DETA and CdS, respectively (Fig. S15). These values approximate their CB positions, allowing the calculation of their valence band (VB) positions: +1.56 V for CdS-DETA and +1.53 V for CdS. The band structures of CdS-DETA and CdS are schematically illustrated (Fig. S16). Cyclic voltammetry (CV) indicates that the potential of 1-phenylethanol oxidation is about +1.51 V (vs. NHE, pH = 7.0, Fig. S17). While both CdS-DETA and CdS hold suitable potentials for 1-phenylethanol oxidation, CdS-DETA exhibits a larger driving force, which contributes to its better oxidation performance.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhotovatalytic Mechanism of CO\u003csub\u003e2\u003c/sub\u003e Reduction Coupled with 1-Phenylethanol Oxidation\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eIn situ\u0026nbsp;\u003c/em\u003eDRIFTS was used to exploit the main intermediates in CO\u003csub\u003e2\u003c/sub\u003e conversion (Fig. 3g). Under dark conditions, the DRIFTS spectra present distinct signals ascribed to protonated ammonium ion (-NH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e) at 1488 and 1634 cm\u003csup\u003e-1\u003c/sup\u003e, as well as carbamate anion (-NH-COO\u003csup\u003e-\u003c/sup\u003e), characterized by the skeletal vibrations (1328 cm\u003csup\u003e-\u003c/sup\u003e\u003csup\u003e1\u003c/sup\u003e), asymmetric and symmetric -COO\u003csup\u003e-\u003c/sup\u003e stretches (1373, 1446, and 1557 cm\u003csup\u003e-1\u003c/sup\u003e), N-H deformation (1543 cm\u003csup\u003e-1\u003c/sup\u003e), and C=O stretching (1685 cm\u003csup\u003e-1\u003c/sup\u003e).\u003csup\u003e41,42\u003c/sup\u003e These spectral features indicate efficient CO\u003csub\u003e2\u003c/sub\u003e chemisorption on CdS-DETA, likely occurring via chemisorption-mediated carbamation of adject primary amines with CO\u003csub\u003e2\u003c/sub\u003e.\u003csup\u003e43-45\u003c/sup\u003e Upon light irradiation, a new signal emerges at 1715 cm\u003csup\u003e-1\u003c/sup\u003e, corresponding to activated CO\u003csub\u003e2\u003c/sub\u003e molecules (*CO\u003csub\u003e2\u003c/sub\u003e).\u003csup\u003e46\u003c/sup\u003e Particularly, the formation of *COOH, a crucial intermediate in CO\u003csub\u003e2\u003c/sub\u003e-to-CO conversion \u003cem\u003evia\u003c/em\u003e *CO\u003csub\u003e2\u003c/sub\u003e protonation, is confirmed by its characteristic signals (1223 and 1623 cm\u003csup\u003e-1\u003c/sup\u003e).\u003csup\u003e47,48\u003c/sup\u003e Concurrently, the presence of adsorbed CO (*CO, 2162 cm\u003csup\u003e-1\u003c/sup\u003e) is detected, indicating its generation from *COOH via proton-coupled electron transfers, accompanied by releasing H\u003csub\u003e2\u003c/sub\u003eO.\u003csup\u003e48\u003c/sup\u003e The accumulation of H\u003csub\u003e2\u003c/sub\u003eO is corroborated by progressively intensified -OH vibration signals (2836 and 2893 cm\u003csup\u003e-\u003c/sup\u003e\u0026sup1;). Moreover, the emergence and gradual enrichment of -NH\u003csub\u003e2\u003c/sub\u003e signals suggest that DETA promotes CO\u003csub\u003e2\u003c/sub\u003e reduction by enriching and freeing *CO\u003csub\u003e2\u003c/sub\u003e species.\u003csup\u003e23\u003c/sup\u003e In contrast, these key species are scarcely noticed on pristine CdS (Fig. S18), underscoring the markedly strengthened CO\u003csub\u003e2\u003c/sub\u003e activation and conversion delivered by DETA.\u003csup\u003e49,50\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo identify the key radicals in 1-phenylethanol oxidation, \u003cem\u003ein situ\u0026nbsp;\u003c/em\u003eEPR tests were carried out using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a radical scavenger. The EPR spectrum obtained under light irradiation in the absence of CO\u003csub\u003e2\u003c/sub\u003e manifests coupling constants (\u0026alpha;\u003csub\u003eN\u003c/sub\u003e = 14.9, \u0026alpha;\u003csub\u003eH\u003c/sub\u003e = 22.1) that align with reported values of the carbon radicals (Fig. 3h).\u003csup\u003e16\u003c/sup\u003e However, these signals are absent under dark conditions, indicating that the oxidative reaction proceeds via a carbon radical-mediated pathway. Furthermore, the liquid chromatography-mass spectrometry (LC-MS) analysis confirms the formation of DMPO-C\u003csub\u003e\u0026alpha;\u003c/sub\u003e radical adduct (Fig. S19), presenting direct evidence for the involvement of the radical intermediate in the oxidation process.\u003c/p\u003e\n\u003cp\u003eDFT calculations were conducted to provide theoretical confirmation for the redox cycles. The CO\u003csub\u003e2\u003c/sub\u003e reduction pathway, mediated by DETA\u0026apos;s terminal -NH\u003csub\u003e2\u003c/sub\u003e groups on the CdS(101) surface follows these key steps (Fig. 4a and Fig. S21): (i) exothermic CO\u003csub\u003e2\u003c/sub\u003e chemisorption (*CO\u003csub\u003e2\u003c/sub\u003e, \u0026Delta;G = -0.22 eV) initiates activation; (ii) proton-coupled electron transfer generates *COOH intermediate (\u0026Delta;G = 0.50 eV); (iii) C-O bond cleavage via the reverse water gas shift-type mechanism yields *CO and *OH; (iv) *OH protonation releases H\u003csub\u003e2\u003c/sub\u003eO, followed by *CO desorption to produce CO gas. The catalytic cycle culminates in active site regeneration, with a moderate energy barrier of 0.60 eV for CO liberation governing the overall reaction kinetics.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe free energy landscape of 1-phenylethanol oxidation consists of the following elementary steps (Fig. 4b): (i, ii) sequential vertical chemisorption of two 1-phenylethanol molecules on CdS (101) with favorable adsorption energies (\u0026Delta;G = -0.79 and -1.05 eV); (iii, v) deprotonation of the adsorbed molecules to form carbon radicals, requiring activation energies of 0.27 and 0.47 eV; (v) radical coupling to generate surface-bound pinacol (\u0026Delta;G = 0.19 eV); (vi) endothermic product desorption (\u0026Delta;G = 0.92 eV), identified as the rate-determining step. Of note, the liberated protons boost CO\u003csub\u003e2\u003c/sub\u003e reduction via proton-assisted electron transfers, closing the catalytic cycle. This mechanistic framework highlights the role of surface-stabilized radical intermediates in controlling the reaction thermodynamics. Moreover, the strong thermodynamic preference of pinacol release over acetophenone desorption (vii, \u0026Delta;G = 1.25 eV, Fig. 4b) explains the excellent selectivity toward pinacol.\u003c/p\u003e\n\u003cp\u003eIn contrast, on bare CdS (Fig. S20), the rate-determining step of CO\u003csub\u003e2\u003c/sub\u003e reduction shifts to H\u003csub\u003e2\u003c/sub\u003eO liberation, requiring a higher energy barrier of 0.8 eV. Meanwhile, the deprotonation of two adsorbed 1-phenylethanol molecules to form carbon radicals for C-C coupling meets much greater energy barriers (1.04 and 0.87 eV), whereas the successive deprotonation of a single 1-phenylethanol molecule for C=O formation proceeds with lower energy barriers (0.58 and -0.34 eV), thus favoring acetophenone production. These findings highlight the effectiveness of DETA decoration in modulating both the reductive and oxidative paths by lowering energy barriers.\u003c/p\u003e\n\u003cp\u003eThe process of collaborative photocatalytic CO\u003csub\u003e2\u003c/sub\u003e reduction integrated with 1-phenylethanol oxidation over CdS-DETA is clarified schematically in Fig. 4c. Upon photoexcitation, CdS generates electron-hole pairs in the conduction and valence bands. Excited holes oxidize 1-phenylethanol to pinacol via radical coupling, simultaneously distributing protons for CO\u003csub\u003e2\u003c/sub\u003e reduction. While the electrons reduce CO\u003csub\u003e2\u003c/sub\u003e to CO by sequential proton-coupled electron transfers, along with H\u003csub\u003e2\u003c/sub\u003eO formation. A minor fraction of excited electrons participate in proton reduction, leading to H\u003csub\u003e2\u003c/sub\u003e evolution. The synergistic interplay between these half-reactions ensures complete deployment of photoinduced carriers, and importantly, DETA increases CO\u003csub\u003e2\u003c/sub\u003e activation and stabilizes key intermediates, empowering marvelous performance in the redox process.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn summary, the efficient coupling of CO\u003csub\u003e2\u003c/sub\u003e reduction with 1-phenylethanol dimerization is realized over diethylenetriamine-decorated CdS in one photoredox system, generating syngas and pinacol simultaneously, with a record-high AQY of 25%, 100% pinacol selectivity, and a unity reaction stoichiometry. The outstanding efficiency is driven by the amine groups, which optimize both the reductive and oxidative paths by lowering energy barriers and meanwhile accelerating the migration kinetics of charge carriers. The underlying mechanism toward the synergetically reinforced syngas and pinacol production is elucidated by \u003cem\u003ein situ\u003c/em\u003e spectroscopic characterizations and theoretical calculations. This work highlights the importance of delicate surface functionalization with organic moieties to optimize redox reaction routes for the co-production of high-value fuels and chemicals using solar energy.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eCadmium nitrate tetrahydrate (Cd(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO), ethanol (anhydrous, 99.7%), acetonitrile (MeCN) and Thiourea (CH\u003csub\u003e4\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003eS) were provided from Sinopharm Chemical Reagent Co., Ltd. Diethylenetriamine (C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e13\u003c/sub\u003eN\u003csub\u003e3\u003c/sub\u003e, 99%) and 1-phenylethanol (C\u003csub\u003e8\u003c/sub\u003eH\u003csub\u003e10\u003c/sub\u003eO, 99%) was purchased from Aladdin. Cadmium acetate dihydrate (Cd(Ac)\u003csub\u003e2\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO) was purchased from Adamas. All the chemicals from commercial sources were used without further purification.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSynthesis of CdS-DETA\u003c/h3\u003e\n\u003cp\u003e2.1347 g of Cd(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO and 2.6338 g of thiourea were added into 50 ml DETA. Then, the mixture solution was stirred at 120\u0026deg;C for 30 min. The product was collected by centrifugation, washed with water and ethanol several times, and finally dried at 70\u0026deg;C.\u003c/p\u003e\n\u003ch3\u003eSynthesis of CdS\u003c/h3\u003e\n\u003cp\u003eCdS was obtained by hydrothermal treatment on CdS-DETA. Specifically, 50 mg CdS-DETA and 50 ml water were added into a 100 ml of Teflon-lined stainless-steel autoclave. After the reaction at 120\u0026deg;C for 12 h, the precipitation was naturally cooled to room temperature and then washed with water and ethanol several times. Afterward, the product was dried at 70\u0026deg;C.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of CdS-DETA-x\u003c/h2\u003e \u003cp\u003e \u003cb\u003ex\u003c/b\u003e represents the mole ratio of DETA/(DETA\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO) in the solvent. Taking CdS-DETA-0.8 as an example, 2.1347 g of Cd(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO and 2.6338 g of thiourea were added into 40 ml of DETA and 10 ml of H2O. Then, the mixture solution was stirred at 120\u0026deg;C for 30 min. The product was collected by centrifugation, washed with water and ethanol several times, and finally dried at 70\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003ePhotocatalytic CO\u003csub\u003e2\u003c/sub\u003e Reduction\u003c/h2\u003e \u003cp\u003eIn a typical photocatalytic carbon dioxide reduction reaction, 5 mg of photocatalyst, 10 ml of acetonitrile, and 500 \u0026micro;l 1-phenylethanol were added into a gas-closed glass reactor. Then, high-purity CO\u003csub\u003e2\u003c/sub\u003e was introduced into the reactor with a partial pressure of 1 atm. A LED lamp (395 nm, 74 mW\u0026middot;cm\u003csup\u003e-\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e) was used as the light source. The temperature of the reaction system was controlled at 25\u0026deg;C by cooling water. During the photocatalytic process, the reaction mixture was vigorously stirred by a magnetic stirrer. After each reaction, the generated gas products were analyzed and quantified by an Agilent 8890 GC, and the liquid products were analyzed and quantified by GC-MS and Liquid chromatography (LC). The cycle experiments were conducted by recovering the used catalysts and then re-dispersing them into a fresh solution for cycling tests, it is worth noting that after each cycle, the catalyst is left in the reactor for 10h for recovery\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was financially supported by the National Natural Science Foundation of China (22372035 and 22302039) and the 111 Project (D16008).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eS.W. conceived and directed the project. X.X. designed the experiments and analyzed the results. M.G. and W.L. conducted theoretical studies. B.S. and M.Z. gave advice on the experiments. X.F.L., C.F., G.Z. and H.Z. participated in the revision of the paper. X.X., W.L. and S.W. prepared the manuscript. 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B Environ\u003c/em\u003e \u003cstrong\u003e320\u003c/strong\u003e, 121985 (2023).\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table","content":"\u003cp\u003eTable 1 is available in the Supplementary Files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":false,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6624021/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6624021/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIntegrating photocatalytic CO\u003csub\u003e2\u003c/sub\u003e reduction with oxidative organic synthesis offers a promising policy for maximizing charge carrier utilization, enabling the simultaneous production of solar fuels and fine chemicals. Herein, highly efficient photoredox catalysis of CO\u003csub\u003e2\u003c/sub\u003e reduction to syngas (CO: 467.1 μmol·h\u003csup\u003e-1\u003c/sup\u003e, H\u003csub\u003e2\u003c/sub\u003e: 78.4 μmol·h\u003csup\u003e-1\u003c/sup\u003e), coupled with 1-phenylethanol oxidation to pinacol (553.9 μmol·h\u003csup\u003e-1\u003c/sup\u003e) is attained over diethylenetriamine modified CdS, delivering a record-high apparent quantum yield of 25%, 100% pinacol selectivity, and a unity reaction stoichiometry. The amine groups effectively modulate both the reductive and oxidative pathways by enhancing CO\u003csub\u003e2\u003c/sub\u003e capture and activation and stabilizing C-centered radicals, respectively. Also, they prompt charge carrier separation and transfer by forming strong Cd-N bonds with CdS. Mechanistic studies reveal that excited holes drive 1-phenylethanol oxidation to pinacol via carbon radical dimerization, while donating protons to boost CO\u003csub\u003e2\u003c/sub\u003e-to-CO reduction via sequential proton-assisted electron transfer processes. This work lights up the route for building advanced artificial photosynthetic systems through precise surface engineering with functional organic groups.\u003c/p\u003e","manuscriptTitle":"Highly efficient photosynthesis of syngas and pinacol from CO₂ and 1-phenylethanol via amine-regulated redox pathways","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-29 06:53:10","doi":"10.21203/rs.3.rs-6624021/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"7741ea1f-f272-4794-ac19-c7011209d0af","owner":[],"postedDate":"May 29th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":49134391,"name":"Physical sciences/Chemistry/Catalysis/Photocatalysis"},{"id":49134392,"name":"Physical sciences/Chemistry/Catalysis/Catalytic mechanisms"}],"tags":[],"updatedAt":"2025-11-24T11:26:29+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-29 06:53:10","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6624021","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6624021","identity":"rs-6624021","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}