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Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
Cycloaddition Reactions: Overview01:16

Cycloaddition Reactions: Overview

Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.
Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
Acid Halides to Alcohols: LiAlH4 Reduction01:19

Acid Halides to Alcohols: LiAlH4 Reduction

Acid halides are reduced to alcohols in the presence of a strong reducing agent like lithium aluminum hydride.
The mechanism proceeds in three steps. First, the nucleophilic hydride ion attacks the carbonyl carbon of the acid halide to form a tetrahedral intermediate. Next, the carbonyl group is re-formed, and the halide ion departs as a leaving group, generating an aldehyde. A second nucleophilic attack by the hydride yields an alkoxide ion, which, upon protonation, gives a primary alcohol as...
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.

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Updated: May 23, 2026

Synthesis and Performance Evaluations of ZnCoS/ZnCdS with Twin Crystal Structure for Multifunctional Redox Photocatalysis in Energy Applications
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Visible light CrO4(2-) reduction using the new CuAlO2/CdS hetero-system.

R Brahimi1, Y Bessekhouad, N Nasrallah

  • 1Centre of Research in Physical and Chemical Analysis (CRAPC), Algiers, Algeria.

Journal of Hazardous Materials
|April 17, 2012
PubMed
Summary

A novel CuAlO(2)/CdS hetero-system effectively reduces hexavalent chromium (Cr(VI)) by 64% under visible light. This photocatalytic process shows high efficiency and stability, offering a promising method for chromium remediation.

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Area of Science:

  • Materials Science
  • Environmental Chemistry
  • Photocatalysis

Background:

  • Hexavalent chromium (Cr(VI)) poses significant environmental and health risks.
  • Developing efficient photocatalysts for Cr(VI) reduction is crucial for environmental remediation.

Purpose of the Study:

  • To investigate the photocatalytic activity of a novel CuAlO(2)/CdS hetero-system for Cr(VI) reduction.
  • To optimize reaction conditions and understand the mechanism of Cr(VI) reduction.

Main Methods:

  • Synthesis of low-doped CuAlO(2) delafossite via sol-gel method.
  • Fabrication of the CuAlO(2)/CdS hetero-system.
  • Photocatalytic reduction experiments under visible light irradiation.
  • Optimization of pH and CuAlO(2) percentage.
  • Identification of reaction products using UV-visible spectrophotometry and linear voltammetry.

Main Results:

  • Achieved 64% reduction of Cr(VI) from an initial concentration of 10(-4) M.
  • The CuAlO(2)/CdS hetero-system demonstrated efficient electron transfer due to its band alignment.
  • Optimized conditions (pH, CuAlO(2) percentage, salicylic acid as hole scavenger) enhanced performance.
  • CuAlO(2) exhibited near 100% photostability at pH 7.5.
  • The photocatalytic process followed pseudo-first-order kinetics with a 2-hour half-life.
  • Cr(3+) was identified as the main reduction product.

Conclusions:

  • The CuAlO(2)/CdS hetero-system is a highly effective photocatalyst for Cr(VI) reduction under visible light.
  • The study provides insights into the mechanism and optimization of photocatalytic Cr(VI) remediation.
  • This approach offers a stable and efficient solution for treating chromium-contaminated water.