H2O2 Triggering Electron-Directed Transfer of Emerging Contaminants over Asymmetric Nano Zinc Oxide Surfaces for Water Self-Purification Expansion

Abstract

Slow mass transfer processes between inert emerging contaminants (ECs) and dissolved oxygen (DO) limit natural water self-purification; thus, excessive energy consumption is necessary to achieve ECs removal, which has become a longstanding global challenge. Here, we propose an innovative water self-purification expansion strategy by constructing asymmetric surfaces that could modulate trace H₂O₂ as trigger rather than oxidant to bridge a channel between inert ECs and natural dissolved oxygen, achieved through a dual-reaction-center (DRC) catalyst consisting of Cu/Co lattice-substituted ZnO nanorods in situ (CCZO-NRs). During water purification, the bond lengths of emerging contaminants (ECs) adsorbed on the asymmetric surface were stretched, and this stretching was further enhanced by H₂O₂ mediation, resulting in a significant reduction of bond-breaking energy barriers. As a result, the consumption rate of H₂O₂ was reduced by two-thirds in the presence of ECs. In contrast, the removal of ECs was increased approximately 95-fold mediated by trace H₂O₂. It exhibits the highest catalytic performance with the lowest dosage of H₂O₂ among numerous similarly reported systems. This discovery is significant for the development of water self-purification expansion technologies.

Scheme 1. Schematic Description of the Reaction Mechanisms of Different ECs Removal Process

(a) Slow water environment self-purification processes. (b) Enhance mass transfer with excess energy consumption in conventional heterogeneous Fenton-like processes. (c) Enhance mass transfer with endogenous energy in DRC catalytic processes. (d) Asymmetric surface expansion of water self-purification capacity triggered by trace H₂O₂.

Figure 1

(a) Illustration of the preparation of the CCZO-NRs. (b) Local details of the XRD patterns of CCZO-NRs and ZO-NRs. (c) HRTEM images of CCZO-NRs. (d) Normalized Cu K-edge X-ray absorption near-edge structure (XANES) spectra of CCZO-NRs and reference samples. (e) k³-weighted Fourier transform extended X-ray absorption fine structure (FT-EXAFS) spectra of CCZO-NRs and reference samples. (f) O 1s XPS spectra of ZO-NRs and CCZO-NRs. (g) shows H₂-TPR curves of the CCZO-NRs and ZO-NRs samples. (h) Illustration of the symmetric surface and asymmetric surface.

Figure 2

(a) Decomposition curves of different ECs in CCZO-NRs suspensions with H₂O₂. (b) Effect of CIP degradation with different concentrations of H₂O₂, different anions, different pH of initial solution, and the cyclic stability of CCZO-NRs system (detailed experimental steps are shown in Methods). (c) 3D-EEM fluorescence spectra of raw wastewater and the water after 120 min of treatment by the CCZO-NRs system. (d) Comparison of normalized k for CIP removal with those of other reported catalysts. (e) Rate of decomposition of H₂O₂ in different suspensions. (f) EPR spectra of CCZO-NRs before and after reaction in different suspensions. (g) Electrochemical impedance spectroscopy (EIS) Nyquist plots of the CCZO-NR electrode. (h) Degradation rate of CIP by the CCZO-NRs system in different gas atmospheres. The inset shows the pseudo-first-order kinetic rate plots of reaction rate. Reaction conditions: natural pH ∼ 7, initial [pollutant] = 10 mg L^–1, initial [H₂O₂] = 10 mM, [catalyst] = 0.2 g L^–1, pH adjustment with HCl and NaOH.

Figure 3

In situ Raman spectra in different suspensions. (a) Process of H₂O₂ adsorption by CCZO-NRs and (b) process of CIP degradation reaction with the CCZO-NRs system. (c) FTIR spectra of CCZO-NRs before and after the reaction in different suspensions. The optimized adsorption configurations of (d) H₂O₂ molecules, (e) phenol molecules, and (f) H₂O₂/phenol molecules on the surface of CCZO-NRs.

Figure 4

(a) Comparison of removal efficiencies of CIP under different quenchers conditions in CCZO-NRs system; (b) ^•OH signals and the relative intensity in different suspensions with BMPO. (c) O₂^•– signals and the relative intensity in different suspensions with BMPO. (d) Reaction path of H₂O₂ decomposition and free energy profile of ^•OH production process (inset corresponding intermediate structures). (e) Bond length of phenol (O–C) in different optimized adsorption configurations. (f) Schematic illustration of the mechanism of water self-purification expansion triggered by H₂O₂ at the asymmetric CCZO-NRs surface.

Figure 5

(a) LC-MS spectrum of intermediates during the reaction. (b) Analysis of intermediate products of CIP degradation in the CCZO-NRs/H₂O₂ suspensions by LC-MS (left inset shows the surface electron density and HOMO orbitals of CIP, respectively). Toxicity assessment of degradation products: (c) logarithm of acute toxicity LC₅₀ of Daphnia (96h) and (d) bioconcentration factor of fish.

Figure 6

(a) H₂O₂ consumption, (b) cost of other chemicals, (c) power consumed, (d) life expectancy, and (e) total cost comparison of the CCZO-NRs system and conventional Fenton process. The red and blue bars correspond to the conventional Fenton process and CCZO-NRs system, respectively.