# Ultrasonic‐Assisted Photocatalytic Conversion of Air to Nitric Acid Under Ambient Conditions

## TL;DR

This paper introduces a new method to efficiently produce nitric acid from air using ultrasound and light, which could benefit sustainable agriculture.

## Contribution

The novel use of ultrasound in photocatalytic conversion of air to nitric acid significantly enhances the synthesis rate and sustainability.

## Key findings

- The synthesis rate of HNO3 reaches 8594 µmol/h/gcat, over 200 times higher than previous methods.
- Using multiple ultrasound sources increases the rate eightfold with nearly 100% selectivity over 700 hours.

## Abstract

The production of nitric acid (HNO3) holds significant importance in the chemical industry, and achieving direct air‐to‐HNO3 conversion with high efficiency and stability under mild conditions remains promising but challenging. Here, we demonstrate an ultrasound‐assisted photocatalytic method in which the generated hydroxyl (·OH) and superoxide (·O2
−) radicals drive the direct synthesis of HNO3 from air under ambient conditions. The synthesis rate of HNO3 is up to 8594 µmol/h/gcat, over 200 times higher than that of previous photocatalytic methods. Using multiple ultrasound sources causes an additional eight times rate enhancement with nearly 100% selectivity maintained over 700 h. The resulting product exhibits comparable fertilization efficacy to conventional fertilizers. By harnessing the UV portion of sunlight that plants do not use, this approach paves the way for full‑spectrum solar energy utilization in sustainable agriculture.

Ultrasound‐assisted photocatalytic air oxidation to nitrate enhances soil nitrogen fertilizer dynamics, thereby enabling improved energy conversion efficiency and sustainable agriculture.