Zinc ions modified InP quantum dots for enhanced photocatalytic hydrogen evolution from hydrogen sulfide

https://doi.org/10.1016/j.jcis.2020.03.110Get rights and content

Highlights

  • Zn2+ modified InP quantum dots (QDs) was prepared under ambient environment by a facile method.

  • Zn2+ could remarkably enhance the photocatalytic efficiency of InP QDs for H2 evolution from H2S.

  • Zn2+ could passivate the surface of InP QDs and promote the charge separation process in the system.

Abstract

Through direct addition of inorganic zinc ions into the solution of indium phosphide quantum dots (InP QDs) at ambient environment, we here present a facile but effective method to modify InP QDs for photocatalytic hydrogen evolution from hydrogen sulfide (H2S). X-ray diffraction patterns and transmission electron microscopic images demonstrate that zinc ions have no significant influence on the crystal structure and morphology of InP QDs, while X-ray photoemission spectra and UV–Vis diffuse and reflectance spectra indicate that zinc ions mainly adsorbed on the surface of InP QDs. Photocatalytic results show the average hydrogen evolution rate has been enhanced to 2.9 times after modification and H2S has indeed involves in the hydrogen evolution process. Steady-state and transient photoluminescence spectra prove that zinc ions could effectively eliminate the surface traps on InP QDs, which is crucial to suppress the recombination of charge carriers. In addition, the electrostatic interaction between zinc ions and the surface sulfide from InP QDs could mitigate the repulsion between QDs and sulfide/hydrosulfide, which may promote the surface oxidative reaction during photocatalysis. This work avoids the traditional harsh and complicated operations required for surface passivation of QDs, which offers a convenient way for optimization of QDs in photocatalysis.

Graphical abstract

Inorganic Zn2+ was modified on the surface of InP QDs by a facile method for enhanced photocatalytic hydrogen evolution from hydrogen sulfide.

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Introduction

Hydrogen sulfide (H2S) is a typical associated gas in oilfield [1]. For example, it is reported that the content of H2S exceeds 90% in some natural gas reserves [2], [3]. For green exploitation of the oil and gas resources, effective removal of H2S is highly demanded [4]. Traditional technique for H2S processing is mainly based on Claus Process, during which H2S is converted into water and elemental sulfur (S) in the end [5]. Unfortunately, hydrogen (H2) energy, the clean energy with high energy density hidden in H2S is wasted. Photocatalytic technology could utilize solar energy to capture H2 from H2S, and hence offers us an alternative method for processing H2S with highly added-value [6], [7].

To effectively capture H2 from H2S, Li et al has studied CdS for photocatalytic H2 evolution from H2S in different reaction media [8]. Subsequently, Kale et al has introduced CdxZn1-xS2, ZnIn2S4, N-doped TiO2/ZnO and etc. for photocatalytic decomposition of H2S in basic KOH solution [9], [10], [11], [12]. Recently, a series of MnS and In2S3 based semiconductors composites have also be exploited [13], [14], [15], [16], [17]. Notably, semiconductor quantum dots (QDs) has emerged as promising photocatatysts during the past years due to their tunable bandgap, large extinction coefficient, large surface-to-volume ratio and rich surface properties [18]. For example, CdSe, CdS and CdTe QDs have all been proved to be highly efficient photocatalysts for H2 evolution in different reaction system [19], [20], [21], [22]. Meanwhile, InP QDs have attracted more and more attention due to their larger intrinsic extinction coefficient and larger Bohr radius with low toxicity [23], [24]. Recently, we have firstly introduced sulfide ion (S2−) capped InP QDs for photocatalytic H2 evolution with ascorbic acid as the electron donor [25]. We prove that the activity of InP QDs is comparable to traditional CdSe QDs, which demonstrates the potential of InP QDs for photocatalytic H2 evolution.

However, further optimization of InP QDs must be carried out to boost the efficiency for potential practical uses. Usually, traps existed on the surface of InP QDs due to the presence of dangling bonds, which is detrimental for charge separation during photocatalysis [26]. Additional growth of ZnS on InP QDs has been proved to eliminate these traps to a certain extent and improve the photocatalytic efficiency. However, growth of ZnS on InP QDs requires strict synthetic condition, which is often under air-free atmosphere with a reaction temperature between 200 and 300 °C in organic solvents with high boiling point [27], [28]. Furthermore, these as-obtained QDs has to go through subsequent ligand change process to remove insulating organic molecules on their surface for effective interaction with the following aqueous photocatalytic reaction environment [25]. Alternatively, we noticed surface modification by Lewis acid or metal ions could be also an effective strategy to adjust the photophysical properties of QDs, which is crucial to the photocatalytic activity of QDs [29], [30], [31].

Here, we report on the facile modification of InP QDs by inorganic zinc ion (Zn2+) under ambient environment to boost photocatalytic H2 evolution from H2S. Introduction of Zn2+ could effectively eliminate the dangling bonds on the surface of InP QDs, which hence mitigates surface photogenerated charge recombination. Moreover, introduction of Zn2+ could neutralize the very negative charged surface of the original InP QDs, which eases the electrostatic repulsion between QDs and S2− (or HS) dissolved in the solution and benefits the oxidative reaction in the system. Photocatalytic tests show that H2 evolution efficiency of the Zn2+ modified InP (Zn-InP) QDs is 2.9 times to that of InP QDs, which manifests the simple but effective strategy to optimize InP QDs for photocatalytic H2 evolution.

Section snippets

Chemicals

Indium chloride hydrate (InCl3·4H2O, 99.9%), zinc idode (ZnI2, 99.999%), tris(diethylamino)phosphine (C12H30N3P, 97.0%), n-hexane (C6H14, 97%), zinc chloride (ZnCl2, ≥98.0%), oleylmine (C18H37N, 80–90%), N-methylformamide (C2H5NO, 99%), formamide (CH3NO, 99%) are from Aladdin (Shanghai, China). Sodium sulfide hydrate (Na2S·9H2O, ≥98.0%), sodium sulfite (Na2SO3, ≥98.0%), zinc nitrate hydrate (Zn(NO3)2·6H2O, ≥99.0%), ethanol (C2H5OH, ≥99.7%), acetone (C3H6O, ≥99.5%) are from Chron Chemicals

Results and discussion

InP QDs were prepared according to our previous report [25] and Zn-InP QDs was obtained by addition of inorganic Zn2+ ions into the formamide solution of InP QDs at ambient environment. Fig. 1 shows the XRD patterns of InP QDs before and after Zn2+ modification. Both samples exhibit wide diffraction peaks at 27.2°, 44.7° and 52.6°, which could be indexed to the {1 1 1}, {2 2 0} and {3 1 1} facets of InP (zinc blende structure, JCPDS 32-0452). The relative wide and weak peaks are consistent with

Conclusions

In summary, our work has developed a facile method to modify InP QDs for photocatalytic H2 evolution from H2S by addition of inorganic Zn2+ under ambient environment. Structure characterization shows that introduction of Zn2+ does not has a significant influence on the original structure of InP QDs; nevertheless, it does improve the photocatalytic activity of InP QDs remarkably, which is probably resulted from the partial elimination of surface dangling bonds on InP QDs and the weak repulsion

CRediT authorship contribution statement

Shan Yu: Conceptualization, Methodology, Investigation, Visualization, Formal analysis, Writing - original draft, Writing - review & editing. Zhanghui Xie: Investigation, Formal analysis, Validation, Visualization, Writing - review & editing. Maoxia Ran: Investigation, Validation. Fan Wu: Investigation. Yunqian Zhong: Writing - review & editing. Meng Dan: Validation. Ying Zhou: Conceptualization, Methodology, Formal analysis, Writing - review & editing, Resources, Funding acquisition,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The author thanks financial support from National Natural Science Foundation of China (U1862111 and U1232119), International Cooperation Project (2017HH0030, and 20GJHZ0145 Sichuan Province, China), and Open Fund (PLN201802 and 201928) of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Southwest Petroleum University, China).

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