Visible-Light Driven H2O-to-H2O2 Reaction by Nitrogen-Enriched Resins for Photocatalytic Oxidation of an Organic Pollutant in Wastewater.

A photocatalytic H2O-to-H2O2 reaction for sustainable organic wastewater treatment is environmentally attractive. Phenolic resins, inexpensive metal-free photocatalysts, are capable of harvesting visible light. Herein, novel nitrogen-enriched resin photocatalysts with a desired band-gap energy (1.83-1.98 eV) for harvesting visible light were prepared by copolymerization of resorcinol and melem for simultaneous photocatalytic H2O-to-H2O2 and oxidation of methylene blue. Under visible light irradiation for 5 h, very high yields of H2O2 (870-975 μM of H2O2/g/h) by RFM resin photocatalysts could be achieved. The photocatalytic H2O2 for reactive oxygen species (•OH) and photogenerated h+ could account for high conversion (40% conversion under visible light irradiation within 3 h) in oxidation of methylene blue. Such unique low-cost metal-free resins demonstrate the visible light photocatalytic H2O-to-H2O2 reaction which can synergize with the oxidation of organic pollutants in wastewater.

Introduction

Persistent organic pollutants (POPs) such as pharmaceuticals, pesticides, and dyes in wastewater could be degraded in an advanced oxidation process (AOP).[1] Hydrogen peroxide (H2O2), being an eco-friendly oxidant, could induce high reactive hydroxide radicals (•OH) for the oxidation of POPs under UV light irradiation.[2] However, H2O2 is generally produced by the anthraquinone method which has the main drawbacks of high energy consumption, complicated operation, potential explosion, and organic solvent pollution.[3] Therefore, the generation of H2O2 from H2O via photocatalysis for the treatment of organic wastewater has received high attention mainly due to the necessity of the green process perspective for sustainable development.[4]

Photocatalysis of H2O to H2O2 by semiconductors such as TiO2, ZnO, BiVO4, and WO3 has been widely studied.[5−10] Largely due to the high recombination rate of photogenerated electrons and holes causing a low conversion efficiency, heteroatom doping, controlling morphology, co-catalyst loading, and heterojunction with other semiconductors have thus been used to improve photocatalytic efficiencies.[11−15] Although many photocatalysts have been used in photocatalytic water splitting, the following improvements are essential for commercialization: (1) Achievement of desired conversion, (2) presence of organic solvents as electron donors, (3) use of inexpensive photocatalysts, and (4) decrease of photocatalyst band-gap energy to <2 eV for visible light irradiation between 400 and 700 nm.[16] A stable and inexpensive metal-free photocatalyst was thus desirable and still challenging.

Resorcinol-formaldehyde (RF), known as a phenolic resin, could be prepared by thermal condensation for applications in drug delivery, catalyst support, super-capacitors, and absorbents.[17−20] The phenolic resins containing a band-gap energy of 1.8–2.0 eV could effectively harvest sunlight for wastewater treatment by photocatalytic oxidation of organic pollutants.[21] Also, the metal-free phenolic resin photocatalyst could be used for the generation of H2O2.[22] It is worth noting that the metal-free resins stably generated H2O2 with 0.5% of solar-chemical conversion, which is comparable to the efficiency for the photocatalytic water splitting by metal-based photocatalysts.[22,23] However, preparation of the resins involves high-temperature and high-pressure reactions. Melem, an active matter in graphitic carbon nitrides (g-C3N4) (GCN), is insoluble in most solvents because of the strong hydrogen bonding in tri-s-triazine that could severely hinder the grafting process with other carbon materials.[24−26] In addition, the melem unit, an active matter in GCN, could form 1,4-endoperoxide intermediates during photocatalysis which induced the formation of H2O2 and suppressed H2O2 decomposition.[27−29] In this work, novel metal-free nitrogen-enriched resins were thus prepared by a simple acidification process. The resorcinol-formaldehyde-melem resin was prepared by the copolymerization of melem and resorcinol under acidic conditions. The resorcinol crosslinked with different monomers (melem and melamine) as the visible light photocatalyst was used in photocatalytic generation of H2O2 and oxidation of organic pollutants in a single compartment. Different nitrogen-enriched monomers for photocatalytic generation of H2O2 and oxidation of a representative organic pollutant in wastewater were studied in the present work. Additionally, the photocatalytic reaction kinetics effected by the resins were also investigated for further engineering applications.

Materials and Methods

Preparation of Resin Photocatalysts

The preparation procedures for the resorcinol-formaldehyde (RF), resorcinol-formaldehyde-melamine (RFm), and resorcinol-formaldehyde-melem (RFM) resins are briefly described in Figure . A solution of resorcinol (R) (Sigma-Aldrich, 99%) and formaldehyde (F) (Acros Organics, 37%) at the R/F molar ratio of 0.5 was mixed in deionized water (40 mL) by stirring at 353 K for 24 min. The solids were washed by acetone to eliminate impurities, filtered, and dried in an oven at 378 K to yield the RF resin.

Figure 1

Preparation procedures for the resin photocatalysts.

To prepare the RFm resin, resorcinol and formaldehyde at the R/F molar ratio of 0.50 were mixed in deionized water (20 mL) under stirring at 313 K for 1 h to form solution A. Melamine (m) (Alfa Aesar, 99%) and formaldehyde at the m/F molar ratio of 0.33 were mixed in deionized water (20 mL) under stirring at 343 K until the solution become colorless to yield B. The clear solution B that was cooled down to 313 K was mixed with solution A for 30 min. The mixed solution was heated at 353 K without stirring for 24 h. The generated solids were washed by acetone to eliminate impurities, filtered, and dried at 378 K to yield brown RFm. The mixed solution containing resorcinol, formaldehyde, and melamine was also heated in a Teflon-lined autoclave at 453 K for 24 h to form the RFm-180 resin for photocatalytic studies.

Because of the strong hydrogen bond in the tri-s-triazine structure, melem (2,5,8-triamino-tri-s-triazine) (M) could not be completely dissolved in most solvents (i.e., water, DMSO, DMF, and methanol) which severely restricted the reaction in the solution with other organic compounds.[30] Nevertheless, melem has three primary amine functional groups in tri-s-triazine for protonation and dissolution with a strong acid. Melem has a high solubility (>385 mg/mL) in sulfuric acid at 298 K without chemical perturbation in the tri-s-triazine of melem, which was revealed by nuclear magnetic resonance (NMR).[24]

Melem was prepared by thermal condensation of melamine (m) at 698 K for 4 h.[31] The RFM resin was prepared by thermal condensation of resorcinol, formaldehyde, and melem with sulfuric acid to have a homogenous copolymerization. Melem and formaldehyde at the M/F molar ratio of 0.33 were mixed under magnetic stirring at 343 K for 1 h to yield solution C. The solution C was cooled down to 313 K and mixed with solution A for 30 min and heated at 353 K without stirring for 24 h. The RFM and RFM-H resins were yielded in the weak (0.1 M) and strong (8 M) acidic H2SO4 solutions, respectively. The suspended solids that were washed with acetone were filtered and dried at 378 K for 24 h.

Characterization of the Resin Photocatalysts

The chemical structure of the resins was studied by solid-state 13C nuclear magnetic resonance (NMR) (Bruker AVANCE III HD) using a 9.4 T magnet. The UV–vis absorption spectra of the resins between 200 and 800 nm were recorded on a Varian Cary 100 diffuse reflectance spectrophotometer. BaSO4 was used as a reference. The band-gap energy of the resin photocatalysts was obtained by the Tauc plot converted from their UV–vis absorption spectra. The crystalline structure of the resins was determined by X-ray diffraction (XRD) (D8 Discover, Bruker AXS Gmbh) under Cu Kα (0.1541 nm) radiation at 40 kV and 40 mA. The morphologies and particle sizes of the photocatalysts were studied by scanning electron microscopy (SEM) (UHRFE-ESM.AURIGA) and transmission electron microscopy (TEM) (JEOL JEM-2100F Cs STEM).

To understand the recombination rate of the photogenerated electrons and holes of the resin photocatalysts, their photoluminescence (PL) spectra were recorded via micro-Raman spectroscopy (Labram HR, France) using a 325 nm wavelength laser as the excitation source. The electrochemical measurements were conducted in a three electrode system using Pt and Ag/AgCl (KCl (3 M)) as the counter and reference electrodes, respectively. The photocatalysts were coated on carbon paper as the working electrodes. The resins (about 50 mg) were mixed with N-methyl-2-pyrrolidone (NMP) (2 mL) containing polyvinylidene difluoride (PVDF) (5 mg) as the binder, which were sonicated for 1 h to form a slurry that was evenly dripped onto a carbon paper and dried at 353 K for 2 h. The electrolyte contains the Na2SO4 (0.1 M) aqueous solution that was purged with nitrogen gas to remove the remaining oxygen before measurements.

Photocatalytic Studies

Photocatalytic H2O-to-H2O2 reactions and oxidation of methylene blue (>89%, Sigma-Aldrich) under visible light irradiation were studied in a cylindrical glass reactor containing the photocatalysts (40 mg) and deionized water (40 mL). Prior to the photocatalytic experiments, the solution in the reactor was purged with oxygen under the dark to reach the adsorption–desorption equilibrium. A 500 W Xe lamp (Burgeon Instrument Co., Ltd.) having the light cutoff at 400 nm was used for photocatalysis at 298 K. To measure the concentration of H2O2, about 1 mL of the aqueous solution from the photocatalytic reactor was periodically sampled, and the solid photocatalysts were separated by filtration using a filter (0.22 μm). Concentrations of H2O2 at pH 5–9 could be determined with benefits of insensitivity to other byproducts in water, high stability of color, and rapid reactivity. The 2,9-dimethy-1,10-phenanthroline (10 mg/mL) (DMP, 98%, Alfa Aesar) solution (0.5 mL), the copper(II) sulfate solution (0.01 M) (0.5 mL), the phosphate buffer solution (0.1 M) (0.5 mL) (pH 7), deionized water (1 mL), and the sample withdrawn from the reactor (1 mL) were mixed in a quartz tube having a 1 cm light pathway.[32] The absorbance of 454 nm was measured on an UV–vis spectrometer (Varian, Cary 100). The decomposition rate of H2O2 (1 mM) effected by the resin photocatalysts (40 mg) under visible light irradiation for 5 h was also measured using the copper-DMP method.

Methylene blue, being a common dyestuff in industry, was used to simulate organic pollutants in wastewater. The resin photocatalysts (40 mg) were dispersed in an aqueous solution (40 mL) containing methylene blue (3 × 10–5 M) under pH 1–9 (adjusted by HCl (1 M) and NaOH (1 M)) in a cylindrical glass reactor. Before the photocatalytic oxidation of methylene blue, the solution was stirred under dark to reach the adsorption equilibrium in the reactor that was then irradiated by a 500 W Xe lamp (Burgeon Instrument Co., Ltd.) having the light cutoff at 400 nm at 298 K. The solution was sampled at a selected period and centrifuged to remove particles from water. The efficiency for the photocatalytic oxidation of methylene blue was studied by measuring the maximum absorbance at 664 nm on the UV–vis absorption spectrometer. To ensure the mineralization of methylene blue, the total organic carbon (TOC) in the reactor was determined on a total organic carbon analyzer (Shimadzu, TOC-L).

Results and Discussion

The XRD patterns in Figure show that the resins have an amorphous structure at a broadened peak (5–30°) centered at 21° corresponding to the (002) plane of graphitic carbon. In addition, the RFM resin has intense peaks centered at 6.2, 12.3, 13.4, 18.5, 23.1, 25.9, 26.7, and 27.5° (2θ) that are related to the crystalline structure of melem (39-1950, JCPDS). Note that the peak at 6.2° is associated with monomer melem.[33] Morphologies of the resins (RFm and RFM) observed by TEM and SEM are shown in Figure . The resins appear in quasi-spheres with particle sizes in the micron scale. The sizes of the RFm and RFM resin are in the range of 20–80 μm. The well distributions of C, N, and O in the resins are also shown in the SEM-mapping spectra (Figure ).

Figure 2

XRD patterns of the (a) RFm, (b) RF, and (c) RFM resins with the crystalline structure of melem (39-1950, JCPDS).

Figure 3

SEM and TEM images of the (a) RFm and (b) RFM resins. The distributions of C, N, and O in the resins are also shown in the SEM-mapping spectra.

The N2 absorption–desorption isotherms and pore size distributions for the RFM, RF, and RFm resins are shown in Figure . The resin photocatalysts exhibit type IV isotherms with H3 hysteresis loops at a high relative pressure range (P/P0 > 0.8) (referred to as the classification of the IUPAC), suggesting the existence of mesopores. Note that the RFM has a relatively high specific surface area and pore volume.

Figure 4

N2 adsorption–desorption isotherms and pore size distributions of the (a) RFM, (b) RF, and (c) RFm resins.

The chemical structure of the resins was studied by 13C NMR spectroscopy. Figure shows that the melem units are crosslinked in the phenolic resin structure to form the RFM resin at the shifts of 164 and 154 ppm which are attributed to C–N2(NH2) and C–N3 in heptazine, respectively.[34] On the other hand, the chemical structure of the RFm resin prepared by crosslinking between melamine and resorcinol is associated with the shift at 166 ppm. The shift at 153 ppm can be attributed to C–OH, suggesting that resorcinol behaves like an electron donor in the resins.[35−37]

Figure 5

13C NMR shifts of the (a) RFM, (b) RFm, and (c) RF resins.

As shown in Figure a, the deconvoluted 13C NMR of the RFM resin has 14 carbon peaks including aromatics, melem units, linkers, and unconnected functional groups between 0 and 180 ppm. The shifts in NMR attributed to the carbon in heptazine are found at 164.6 and 155.0 ppm (#1 and 2). Carbon by being substituted or without being substituted in aromatics is observed at 153.1, 131.5, 122.2, 117.8, 111.4, and 105.2 ppm (#3–8). The carbon shifts (#9, 12–14) of linkers as bridge in polymers, i.e., methylene ether, methylene and linkers between aromatic and heptazine appear at 70.7, 29.5, 19.7, and 54.5 ppm, respectively. Noncrosslinked methylol groups (C–OH) remained on the resorcinol, and melem units are related to the shifts at 60.0 and 65.9 ppm, respectively (#10, 11).

Figure 6

Deconvolution of 13C NMR shifts for the (a) RFM and (b) RFm resins. Heptazine C–N2(NR2) [164.6 ppm, 1], Heptazine C–N3 [155.0 ppm, 2], resorcinol C–OH [153.1 ppm, 3], nonreplaced resorcinol C [131.5ppm, 4; 111.4ppm, 7; 105.2 ppm, 8], replaced resorcinol C [122.2 ppm, 5; 117.8 ppm, 6], methylene ether linker −C–O–C– [70 ppm, 9], methylene linker [30.0 ppm,13; 20.0 ppm, 14], methylol C–OH [65.9 ppm, 10; 60.0 ppm, 11], and linker N–C–C [54.5 ppm, 12], triazine C–N3 [167.0 ppm, 15], resorcinol C–OH [153.1 ppm, 16], nonreplaced resorcinol C [129 ppm, 17; 110.4 ppm, 19; 104.0 ppm, 20], replaced resorcinol C [117.5 ppm, 18], methylene ether linker −C–O–C– [72.1 ppm, 21], methylene linker [30.7 ppm, 25; 18.8 ppm, 26], methylol C–OH [67.3 ppm, 22; 63.4 ppm, 23], and linker N–C–C [52.1 ppm, 24].

Compared to the NMR shifts of the RFM resin, the melem carbon groups are substituted by the shifts of melamine at 167 ppm (see Figure b). The NMR shifts of aromatics, linkers, and residual functional groups (#3–14) for the RFm resin similarly correspond to those of the RFM resin (#18–26). However, the NMR shifts at similar positions of carbon components for the RFM and RFm resins are slightly different, which may be attributed to the variance in the molecular structure and electron migration property between melem and melamine.

Figure A shows that the UV–vis diffuse reflectance spectra of the resins have an intense absorbance between 200 and 700 nm, suggesting that the resin photocatalysts can harvest visible light. The band-gap energy of the resins was studied by the Tauc plot (see Figure B) obtained from the absorption spectra. The RF, RFM, and RFm resins have a band-gap energy of 1.98, 1.88, and 1.83 eV, respectively. It seems that the band-gap energy of the resins decreases by incorporating nitrogen-enriched units, such as melem and melamine. The band-gap energy could be affected by many factors such as the size of sp2 clusters, distortion of π state, and sp2/sp3 contents.[38] The red-shifts for the RFM and RFm resins could be attributed to the formation of a mid-gap during the copolymerization process associated with the sp2/sp3 rehybridization of carbon atoms in the resorcinol and nitrogen-enriched units.[38,39] In Figure C, the PL spectra of the resin photocatalysts were obtained under an excitation wavelength of 325 nm. The emission wavelengths of the resin-based photocatalysts are in the range of 400–700 nm. The PL intensities of the RFm and RFM decrease by incorporating melem units (melem and melamine), suggesting that the formation of tri-s-triazine (heptazine) structures by thermal condensation of melamine may reduce the recombination rate of photogenerated electrons and holes.

Figure 7

(A) UV–vis diffuse reflectance spectra, (B) Tauc plots, and (C) PL spectra of the (a) RFm, (b) RFM, and (c) RF resins.

Figure A shows the electrochemical impedance spectra (EIS) of the resins that have relatively low charge resistances, which are supportive of photocatalytic reactions. The flat band potential of the resins was measured at a fixed frequency of 500 Hz on the electrochemical three-electrode system. The resins are typical n-type semiconductors observed from the slope of the Mott–Schottky plot. The flat band potential determined by the X-intercept in the linear region of the Mott–Schottky plot was converted to common potential representation related to the normal hydrogen electrode (NHE). In Figure C, the band-gap energy levels of the resins are established by the combination of the band-gap energy and the flat band potential that are obtained from the Tauc and Mott–Schottky plots, respectively. The reaction potentials for two-electron reduction of oxygen (0.68 V) and oxidation of water (1.23 V) are located within the band-gap energy level of the resins, suggesting that the resin photocatalysts are feasible for facilitating the photocatalytic H2O-to-H2O2 reactions.

Figure 8

(A) Mott–Schottky plots, (B) EIS for the Nyquist plots, and (C) energy band levels of the (a) RF, (b) RFM, and (c) RFm resins.

Photocatalytic H2O-to-H2O2 Reaction

A calibration curve for H2O2 concentrations related to the corresponding absorbance at 454 nm using the copper-DMP method for the determination of H2O2 concentration from photocatalytic generation and decomposition was developed. Figure A shows the time-dependent photocatalytic H2O-to-H2O2 reaction by the resins. The RFM is more effective than the RF and RFm under the visible-light irradiation. In the presence of the RFM resin (40 mg), accumulated 174 μM of H2O2 (see Table ) under the 5 h visible-light irradiation (i.e., 870 μM of H2O2/g/h) could be obtained. Melem, being the main active matter, could be transformed to 1,4-endoperoxide species during photocatalysis which further induced the formation of H2O2.[36] Additionally, one-electron transfer of the O2 reaction (O2 → H2O) could be effectively suppressed by heptazine during light irradiation.[40]

Figure 9

Time-dependent photocatalytic (A) formation and (B) decomposition of H2O2 effected by the (a) RFM-H, (b) RFM, (c) RF, (d) RFm-180, and (e) RFm resins.

Table 1

Rate Constants for Photocatalytic H2O2 Formation (kf) and Decomposition (kd) by the Resin Photocatalysts

resins	accumulated H2O2 (μmol)	kf (μM min–1)	kd (min–1)
RFM-H	195	0.65	0.0023
RFM	174	0.58	0.0019
RF	134	0.44	0.0016
RFm-180	109	0.36	0.0013
RFm	65	0.21	0.0008

With an increase of the acidic concentration to 8 M (H2SO4) during the copolymerization process, the photocatalytic H2O2 yield could further be improved, i.e., 975 μM H2O2/g/h (accumulated 195 μM of H2O2) (Table ) for the 5 h visible-light irradiation by the RFM-H resin (see Figure ). The better photocatalytic H2O2 yield by the RFM-H resin may be related to the sulfur-mediated copolymerization which potentially influences texture, electronic and optical properties of the resin. The triazine units seem to be an inactive matter in the RFm resin. Compared to the heptazine structure, triazine has a less ability to induce formation of 1, 4-endoperoxide species.

After the hydrothermal treatment of the RFm resin at 453 K for 24 h, the generated RFm-180 resin with more conducting structure could increase the photocatalytic H2O2 yield by 68% if compared with the RFm (accumulated 65 μmol H2O2) (Table ). Yet, the photocatalytic H2O2 yield by the RFm-180 resin was less than that by the RF one, suggesting that the triazine unit could distort the inherent phenolic resin structure, which caused a rapid recombination of photogenerated electrons and holes.

The photocatalytic H2O-to-H2O2 reaction may also involve the decomposition of H2O2. The reaction kinetics for photocatalytic H2O2 formation (kf) and decomposition (kd) were thus studied. Generally, the H2O2 formation and decomposition rates could be governed by the pseudo-zero-order and pseudo-first-order reaction kinetics, respectively. By the Equation ([H2O2] = (kf/kd)(1 – exp(−kdt))), the reaction rate constants for the resin photocatalysts could be obtained (see Table ). As shown in Figure A, the RFM resin with the incorporation of melem accounts for more photocatalytic H2O2 yields under the visible-light irradiation than the RF and RFm ones. For the photocatalytic H2O-to-H2O2 reaction, the relatively high H2O2 formation kf accompanies with a high H2O2 decomposition kd, having the H2O2 formation equilibrium constant of 280 μM approximately.

Methylene blue, being a representative dye in industry, was used as an organic model pollutant for studying photocatalytic oxidation effected by the resins under the visible light irradiation (λ > 400 nm) at 298 K. The time-dependent photocatalytic oxidation of methylene blue (3 × 10–5 M) effected by the RF, RFm, and RFM resins is shown in Figure . The RFM resin photocatalyst that accumulated 174 μM of H2O2 (see Table ) under the 5 h visible-light irradiation has a relatively high reaction rate (pseudo-first-order) for photocatalytic oxidation of methylene blue. Correspondingly, the removal efficiency of TOC for photocatalytic oxidation of methylene blue under the 3 h visible-light irradiation by the RFM resin is 38% that is greater than those by the RF and RFm resins. A similar performance for the photocatalytic H2O-to-H2O2 reaction by the resin photocatalysts was also observed. The photocatalytic H2O2 may play a critical role in oxidation of methylene blue.

Figure 10

(A) Time-dependent photocatalytic oxidation of methylene blue (3 × 10–5 M) by the RF, RFm, and RFM resins and (B) pseudo-first order rate constant plots for the resins. (Inset in (A): TOC removal efficiencies for photocatalytic oxidation of methylene blue under the 3 h visible-light irradiation).

Reactive oxygen species (ROS) being oxygen-containing radicals are capable of independent existence with one or more unpaired electrons. Reactive oxygen species are often expanded to include reactive oxygen-containing compounds without unpaired electrons, such as H2O2. Photocatalytic oxidation of methylene blue could involve direct oxidation by photogenerated holes (h+) and ROS (H2O2, hydroxyl free radicals (•OH) and superoxide free radicals (•O2–)). The reduction potentials of the strong ROS such as H2O/•OH (2.7 V vs NHE) and O2/•O2– (0.1 V vs NHE) are not within the band-gap energy level of the resins between 0.28 and 2.39 V (see Figure ), suggesting that the formation of free radical ROS from H2O and O2 may be unfavorable during light irradiation. However, the photocatalytic H2O-to-H2O2 reaction for H2O2/•OH (0.38 V vs NHE) and photogenerated h+ could account for the oxidation of methylene blue.

Other factors (such as pH) on the H2O-to-H2O2 converting efficiency and methylene blue oxidation performance were thus considered. The effect of pH (1–9 adjusted by HCl (1 M) and NaOH (1 M)) on the photocatalytic H2O-to-H2O2 reaction and oxidation of methylene blue by the RFM resin is shown in Figure . At pH 1.0–2.6, the accumulated H2O2 is about 250 μM within the 5 h irradiation by RFM and decreases to 180 μM of H2O2 as the pH increases to 6.8–9.0. Accordingly, H+ can prompt the photocatalytic H2O-to-H2O2 reaction. In the presence of high concentration H2O2 with the induced ROS (•OH), methylene blue could be effectively oxidized (40–80% approximately) by the RFM resin at pH 1–4. At pH 4–9, as the photocatalytic H2O2 yields decrease, the photogenerated h+ could alternatively account for the steady conversion (40%) for oxidation of methylene blue.

Figure 11

Effect of pH on the photocatalytic H2O-to-H2O2 reaction and oxidation of methylene blue (3 × 10–5 M) by the RFM resin under the visible-light irradiation for 5 h.

Conclusions

A novel nitrogen-enriched resin with the desired band-gap energy (1.83–1.98 eV) for harvesting visible light was prepared using a simple method for the simultaneous photocatalytic H2O-to-H2O2 reaction and oxidation of methylene blue. Under visible light irradiation for 5 h, very high yields of H2O2 (870–975 μM H2O2/g/h) by the RFM resin photocatalysts could be achieved. The photocatalytic H2O2 reaction for ROS (•OH) and photogenerated h+ could account for the high conversion (40% within a 3 h visible-light irradiation) in oxidation of methylene blue. Such unique low-cost metal-free resins demonstrate the visible-light photocatalytic H2O-to-H2O2 reaction, which can synergize with oxidation of organic pollutants in wastewater.