Hu et al. 2023 - CdIn2S4/In2S3 photocatalytic Cr(VI) reduction
Hu and colleagues synthesized CdIn2S4/In2S3 heterojunction photocatalysts and tested visible-light reduction of synthetic aqueous Cr(VI). This is primary remediation/testing evidence, not food, ingredient, drinking-water occurrence, or product evidence. The routeable facts are the defined synthetic Cr(VI) challenge concentration, catalyst loading, reaction-rate constants, and near-complete Cr(VI) reduction time for the optimal 0.5 CISI composite.
Key numbers
Cr(VI) reduction protocol
The photocatalytic assay used a 300 W xenon arc lamp with visible-light cutoff at lambda > 420 nm. For each run, 10.0 mg photocatalyst and 1 mL citric acid at 100 mg/L were added to 100 mL of 20 mg/L Cr(VI) solution. The suspension was stirred for 30 minutes in the dark to reach adsorption-desorption balance, then irradiated under visible light. Samples were taken every 15 minutes. Residual Cr(VI) was quantified by the 1,5-diphenylcarbazide colorimetric method at approximately 540 nm.
Reaction rate constants
Figure 8 reports Cr(VI) photoreduction curves and kinetic fits. The reaction-rate constants were:
| Photocatalyst | Cr(VI) photoreduction rate constant (min^-1) |
|---|---|
| CdIn2S4 (CIS) | 0.03554 |
| In2S3 (IS) | 0.05578 |
| 0.75 CISI | 0.09358 |
| 0.25 CISI | 0.13313 |
| 0.5 CISI | 0.15561 |
The optimal 0.5 CISI sample had the highest rate constant and almost completely removed Cr(VI) within 45 minutes. The authors attribute the higher activity to the 2D/2D heterojunction interface between CdIn2S4 and In2S3, which improves charge separation and transfer.
Comparator table
Table 1 compares the 0.5 CISI run with literature photocatalysts. The “this work” entry used 10 mg catalyst, 20 mg/L Cr(VI), 100 mL solution, and 45 minutes. Comparators listed in the paper required 15-200 mg catalyst, 10-70 mg/L Cr(VI), 30-500 mL solution, and 50-180 minutes.
Catalyst characterization
The CdIn2S4 and In2S3 components were synthesized by reflux/one-pot methods. XRD, SEM, TEM, HRTEM, STEM-HAADF, EDS mapping, UV-vis DRS, XPS, PL, time-resolved PL, EIS, transient photocurrent response, LSV, and Mott-Schottky measurements were used to characterize the catalysts. The 0.5 CISI composite showed Cd, In, and S in elemental mapping; XPS Cd 3d peaks for CIS appeared at 411.8 eV and 405.1 eV. Cycling tests showed that 0.5 CISI retained high photocatalytic efficiency over five cycles, with XRD and SEM indicating structural stability after Cr(VI) reduction.
Methods (brief)
In2S3 was prepared from InCl3.4H2O and thioacetamide in water at 90 C for 5 hours. CdIn2S4 was prepared from cadmium acetate dihydrate, InCl3.4H2O, and thioacetamide at 100 C for 12 hours. CdIn2S4/In2S3 composites with x = 0.25, 0.5, and 0.75 In2S3 molar ratios were synthesized similarly in one pot. Photocatalytic Cr(VI) reduction was performed in synthetic 20 mg/L Cr(VI) solution with citric acid as a sacrificial agent and visible-light irradiation; Ct/C0 was used as the reduction metric.
Implications
Certification: This source does not support HMTc product or ingredient standards. It uses a synthetic Cr(VI) challenge solution and a cadmium-containing semiconductor photocatalyst under laboratory conditions.
Courses: Useful remediation-method example for Cr(VI) reduction and for separating chromium speciation. The experiment targets hexavalent chromium reduction to lower-toxicity chromium species, rather than measuring total chromium occurrence.
App: Route to testing/remediation context and Cr(VI) metal context. Do not route the 20 mg/L challenge solution as drinking-water occurrence, and do not treat catalyst Cd as a consumer-product cadmium concentration.
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Verification notes
The PDF has author attribution and DOI 10.3390/catal13050826; no DOI conflict was observed. The Cr(VI) values are from a synthetic laboratory challenge solution, not natural water, food, or product occurrence. Cadmium appears as a component of the CdIn2S4 photocatalyst and in catalyst characterization; the paper does not report cadmium contamination in the treated water or in consumer goods.
Page history
The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.
| Commit | Date | Description |
|---|---|---|
| c1aef38 | 2026-06-02 | audit-queue: hamid2021-bacterial-plant-biostimulants-review → audited-promote |