Studying chemical processes at the air–water interface is always challenging. A recent report claimed that H2O2 was formed spontaneously on the surface of condensed water microdroplets. However, a newer report concluded that the detected H2O2 in the previous report could originate in part from the water vapor source that involved ultrasonic atomization of liquid water. Here, this phenomenon is reinvestigated regarding the influence of ultrasonic cavitation, surface modification of droplets, and solutes in the bulk liquid on H2O2 production. When the droplet surfaces were modified by surfactants, H2O2 production did not change, whereas adding gases or inorganic compounds to the bulk solution caused significant changes in H2O2 production. These results confirm that H2O2 formation originates from cavitation in bulk solutions. It is concluded that the air–water interface of water microdroplets itself does not generate H2O2.

Recent claims of the spontaneous H 2 O 2 formation at the air−water interface of water microdroplets have sparked debates on its feasibility. New results from different research groups have provided more insight into these claims, but conclusive proofs are still far from realized. In this Perspective, thermodynamic viewpoints, potential experiments, and theoretical approaches are presented as references for future studies. We suggest that future work should seek for H 2 byproduct as indirect evidence to confirm the feasibility of this phenomenon. Examining potential energy surfaces for H 2 O 2 formation reaction when moving from the bulk to the interface under the influence of the local electric fields is also critical to establish this phenomenon.

Metrics & MoreArticle Recommendations * sı Supporting Information ABSTRACT: "On-water" catalysis, the unusual activity of water molecules at the organic solvent−water interface, has been demonstrated in many organic reactions. However, the catalytic mechanism has remained unclear, largely because of the irreproducibility of the organic−water interface under the common stirring condition. Here, the interfacial area was controlled by employing adsorbed water on mesoporous silica nanoparticles as the catalyst.Reliable kinetics of the cycloaddition reaction of quadricyclane and diethyl azodicarboxylate (DEAD) at the toluene−water interface within the nanoparticle pores were measured. Data reveal an Eley−Rideal mechanism, wherein DEAD adsorbs at the toluene−water interface via hydrogen bonds formed with interfacial water, which lower the activation energy of the cycloaddition reaction. The mechanistic insights gained and preparation of surface water in silica pores described herein may facilitate the future design of improved "on-water" catalysts.Letter pubs.acs.org/JPCL

In this study, a composite material (ACS) was successfully synthesized from activated carbon (AC) derived from soybean curd and sludge from the supply water treatment process using FeCl3. Subsequently, the ACS was employed as a heterogeneous catalyst for the degradation of Paracetamol (PRC) in solutions under conditions of the Fenton process. The conditions for synthesizing composite material were evaluated under different temperatures (200 to 900oC) and AC/sludge ratios. Effects of pyrolysis temperature and of reaction parameters (pH, contacting time) were evaluated under batch conditions based on the degradation efficiency of PRC and TOC. PRC and TOC were analyzed using HPLC and TOC instrument. Results showed that the composite material synthesized at 600oC with AC/sludge = 1/1 (w/w) was of the best performance on the removal of PRC (95% after 30 min). At pH 2 and 3, the PRC removal efficiency was 89% and 18% after 15 minutes and 95% and 54% after 30 minutes, respectively, which were significantly higher than those obtained at higher pH values. After 24 hours, the PRC removal efficiency was 99% and the TOC removal efficiency reached 95%. The results indicated that high efficiency was obtained by synthesized material and most of PRC was converted to simple and non-toxic compounds such as CO2 and H2O.