Ammonia is an important chemical raw material and non-carbon-based fuel. Photocatalytic ammonia production technology as a mild alternative to the traditional Harbor–Bosch route is carried out at the air, liquid, and solid three-phase interface. Promoting the activation of N₂, depressing hydrogen evolution reaction (HER), and increasing the local N₂ concentration around the catalyst surface are critical factors in achieving high conversion efficiency. In this paper, we proposed that defective TiO₂ is surface-modified by alkyl acids with different carbon chain lengths (C₂, C₅, C₈, C₁₁, and C₁₄) to tune the catalyst surface properties. The defect sites greatly promote N₂ adsorption and activation. The wettability of the catalyst can be regulated from hydrophilic to hydrophobic by the length of the alkyl chain. The hydrophobic surface enhances the N₂ adsorption and increases the local N₂ concentration due to its aerophile. Meanwhile, it depresses the proton adsorption and HER. Overall, the nitrogen reduction reaction (NRR) is greatly promoted. Among the series of samples, they present a systematic change and have a maximal NRR performance for n-octanoic acid-defective TiO₂ (C₈-Vo-TiO₂; Vo = oxygen vacancy). The rate of ammonia production can be as high as 392 μmol·g⁻¹·h⁻¹. This work provides a new strategy for efficient ammonia synthesis at the three-phase interface using photocatalyst technology.

The solar H₂ generation directly from natural seawater is a sustainable way of green energy. However, it is limited by a low H₂ generation rate even compared to fresh water. In this report, TiO₂ is chosen as a model photocatalyst to disclose the critical factor to deteriorate the H₂ generation rate from seawater. The simulated seawater (SSW), which is composed of eight ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, Br⁻, SO₄²⁻, and CO₃²⁻), is investigated the effect of each ion on the H₂ production. The results indicate that all ions have a negative effect at the same concentration as in the seawater except Br⁻. The CO₃²⁻ has the most serious deterioration, and the H₂ production rate lowers near 40% even at [CO₃²⁻] of 1.5 mmol·L⁻¹. The H₂ production rate can be recovered to 85% if the CO₃²⁻ is excluded from the SSW. To understand the reason, the zeta potential of the TiO₂ treated with different ions aqueous solution reveals that the zeta potential decreases when it is treated with CO₃²⁻ and SO₄²⁻ due to they can adsorb on the surface of TiO₂ nanoparticles. Fourier transform infrared (FTIR) and thermogravimetric analysis-mass spectroscopy (TGA-MS) further confirm that the adsorbed ion is mainly from CO₃²⁻. Since the pH of seawater is about 8.9 between pK_a1 (6.37) and pK_a2 (10.3) of H₂CO₃, the CO₃²⁻ should exist in the form of HCO₃⁻ in the seawater. We proposed a simple method to remove the adsorbed HCO₃⁻ from the TiO₂ surface by adjusting the pH below the pK_a1. The results indicate that if a trace amount of HCl (adjusting pH ~ 6.0) is added to the SSW, the H₂ production rate can be recovered to 85% of that in pure water.

Optimizing photocatalytic CO₂ reduction with simultaneous pollutant degradation is highly desired. However, the photocatalytic efficiency is restricted by the unmatched redox ability, high carriers’ recombination rate, and lack of reactive sites of the present photocatalysts. Herein, the CuInZnS-Ti₃C₂T_x hybrid with matched redox ability and suitable CO₂ adsorption property was rationally synthesized. The nucleation and growth process of CuInZnS was interfered by the addition of Ti₃C₂T_x with a negative charge, resulting in thinner nanosheets and richer reactive sites. Besides, the Schottky heterojunction built in the hybrid simultaneously improved the photoexcited charge transfer property, sunlight absorption range, and CO₂ adsorption ability. Consequently, upon exposure to sunlight, CuInZnS-Ti₃C₂T_x exhibited an efficient photocatalytic CO₂ reduction performance (10.2 μmol·h⁻¹·g⁻¹) with synergetic tetracycline degradation, obviously higher than that of pure CuInZnS. Based on the combination of theoretical calculation and experimental characterization, the photocatalytic mechanism was investigated comprehensively. This work offers a reference for the remission of worldwide energy shortage and environmental pollution problems.

To perform the electrochemical nitrogen reduction reaction (NRR) under milder conditions for sustainable ammonia production, electrocatalysts should exhibit high selectivity, activity, and durability. However, the key restrictions are the highly stable N≡N triple bond and the competitive hydrogen evolution reaction (HER), which make it difficult to adsorb and activate N₂ on the surface of electrocatalysts, leading to a low ammonia yield and Faraday efficiency. Inspired by the enzymatic nitrogenase process and using the Fe-Mo as the active center, here we report supported Fe₂Mo₃O₈/XC-72 as an effective and durable electrocatalyst for the NRR. Fe₂Mo₃O₈/XC-72 exhibited NRR activity with an NH₃ yield of 30.4 μg·h⁻¹·mg⁻¹ (−0.3 V) and a Faraday efficiency of 8.2% (−0.3 V). Theoretical calculations demonstrated that the electrocatalytic nitrogen fixation mechanism involved the Fe atom in the Fe₂Mo₃O₈/XC-72 electrocatalyst acting as the main active site in the enzymatic pathway (*NH₂ → *NH₃), which activated nitrogen molecules and promoted the NRR performance.

Electrochemical reduction of nitrogen to ammonia under mild conditions provides an intriguing approach for energy conversion. A grand challenge for electrochemical nitrogen reduction reaction (NRR) is to design a superior electrocatalyst to obtain high performance including high catalytic activity and selectivity. In the NRR process, the three most important steps are nitrogen adsorption, nitrogen activation, and ammonia desorption. We take MoS₂ as the research object and obtain catalysts with different electronic densities of states through the doping of Fe and V, respectively. Using a combination of experiments and theoretical calculations, it is demonstrated that V-doped MoS₂ (MoS₂-V) shows better nitrogen adsorption and activation, while Fe-doped MoS₂ (MoS₂-Fe) obtains the highest ammonia yield in experiments (20.11 µg·h^-1·mg_cat^–1.) due to its easier desorption of ammonia. Therefore, an appropriate balance between nitrogen adsorption, nitrogen activation, and ammonia desorption should be achieved to obtain highly efficient NRR electrocatalysts.

To further understand the effect of structural defects on the electrochemical and photocatalytic properties of TiO₂, two synthetic approaches based on hydrothermal synthesis and post-synthetic chemical reduction to achieve oxygen defectimplantation were developed herein. These approaches led to the formation of TiO₂ nanorods with uniformly distributed defects in either the bulk or on the surface, or the combination of both, in the formed TiO₂ nanorods (NRs). Both approaches utilize unique TiN nanoparticles as the reaction precursor. Electron microscopy and Brunauer-Emmett-Teller (BET) analyses indicate that all the studied samples exhibit similar morphology and similar specific surface areas. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) data confirm the existence of oxygen defects (VO). The photocatalytic properties of TiO₂ with different types of implanted VO were evaluated based on photocatalytic H₂ production. By optimizing the concentration of VO among the TiO₂ NRs subjected to different treatments, significantly higher photocatalytic activities than that of the stoichiometric TiO₂ NRs was achieved. The incident photon-to-current efficiency (IPCE) data indicate that the enhanced photocatalytic activity arises mainly from defect-assisted charge separation, which implies that photo-generated electrons or holes can be captured by VO and suppress the charge recombination process. The results show that the defective TiO₂ obtained by combining the two approaches exhibits the greatest photocatalytic activity enhancement among all the samples.