Spontaneous Formation of Low Valence Copper on Red Phosphorus to Effectively Activate Molecular Oxygen for Advanced Oxidation Process.

Efficient spontaneous molecular oxygen (O2) activation is an important technology in advanced oxidation processes. Its activation under ambient conditions without using solar energy or electricity is a very interesting topic. Low valence copper (LVC) exhibits theoretical ultrahigh activity toward O2. However, LVC is difficult to prepare and suffers from poor stability. Here, we first report a novel method for the fabrication of LVC material (P-Cu) via the spontaneous reaction of red phosphorus (P) and Cu2+. Red P, a material with excellent electron donating ability and can directly reduce Cu2+ in solution to LVC via forming Cu-P bonds. With the aid of the Cu-P bond, LVC maintains an electron-rich state and can rapidly activate O2 to produce ·OH. By using air, the ·OH yield reaches a high value of 423 µmol g-1 h-1, which is higher than traditional photocatalytic and Fenton-like systems. Moreover, the property of P-Cu is superior to that of classical nano-zero-valent copper. This work first reports the concept of spontaneous formation of LVC and develops a novel avenue for efficient O2 activation under ambient conditions.

Low-valent copper on molybdenum triggers molecular oxygen activation to selectively generate singlet oxygen for advanced oxidation processes.

Singlet oxygen (1O2), which is difficult to generate, plays an important role in chemosynthesis, biomedicine and environment. Molecular oxygen (O2) is a green oxidant to produce 1O2 cost-effectively. However, O2 activation is difficult due to its spin-forbidden nature. Moreover, the main products of O2 activation are basically hydrogen peroxide (H2O2) and hydroxyl radical (•OH), but rarely 1O2. Herein, we innovatively realize the selective generation of 1O2 via O2 activation by a facile molybdenum (Mo)/Cu2+ system. In this system, Mo firstly reduces Cu2+ in solution to low-valence Cu0/Cu+ on its surface. Cu0/Cu+ activates O2 to generate superoxide radical (O2•-). Importantly, O2•- can be captured immediately and oxidized to 1O2 by surface-bound Mo6+ rather than reduced to H2O2. As a result, the Mo/Cu2+ system can selectively produce 1O2. Under air and O2 conditions, the degradation efficiency of ibuprofen by Mo/Cu2+ system is 67.2 % and 76.6 %, respectively. The degradation efficiencies of bisphenol A, rhodamine B and furfuryl alcohol are 77.1 %, 87.7 % and 91.1 %, respectively. The dosages of Mo and Cu2+ are 0.4 g/L and 3 mM, respectively, and the reaction time is 2 h. Interestingly, the activity of Mo decreased by only 4.2 % after 4 cycles. Therefore, this study provides a green pathway to selectively generate 1O2 for advanced oxidation processes.

Rust triggers rapid reduction of Cr6+ by red phosphorus: The importance of electronic transfer medium of Fe3.

Red phosphorus (P) is one of the metalloid materials, with five external electrons, it should be an excellent electron donor. However, the activity of red P to reduce Cr6+ is limited. Due to electrostatic repulsion, it is difficult for the electrons on the red P to transfer to the chromate anion (Cr6+). Interestingly, we found that Fe3+ derived from rust, waste iron or Fe3+ reagents can be used as the electron transport medium to solve the electron transport obstacles between red P and Cr6+. As a result, the reduction of Cr6+ by red P/rust system takes only 20 min, which is far lower than the 140 min of red P. The reduction rate of Cr6+ in the red P/rust system is about 12.3 times that of red P. The reaction mechanism is that red P is not easy to access chromate anions but can easily adsorb Fe3+. The adsorbed Fe3+ will be reduced to Fe2+ by red P, and the regenerated Fe2+ will diffuse into the solution to rapidly reduce Cr6+. Therefore, this work provides an alternative waste iron reuse pathway and also sheds light on the important role of electron medium in reduction reaction.