Photocatalytic Hydrogen Production Rate Research Articles

In Situ XPS Proved Efficient Charge Transfer of S‐Scheme Heterjunction Based on Graphdiyne (g‐CnH2n‐2) Nanosheets Coupling with Semi‐Crystalline NiCo2S4 for Efficient Photocatalytic H2 Evolution

AbstractThe excessive utilization of fossil fuels has resulted in an energy crisis. The implementation of a heterojunction for photocatalytic hydrogen evolution represents a promising solution to the current energy predicament. In this work, a 0D/2D S‐scheme graphdiyne/NiCo2S4 (GDY/NiCo2S4) heterojunction is constructed by semi‐crystalline NiCo2S4 nanoparticles (NPs) immobilized on the surface of GDY nanosheets through hydrothermal method. Atomic force microscopy (AFM) demonstrated the thickness of GDY nanosheets is 2.8 nm. The unique 2D laminar structure and porous structure of GDY ensures a tight bond with NiCo2S4 NPs. The maximum rate of photocatalytic hydrogen production is 6682.6 µmol h−1 g−1 over 15% GDY/NiCo2S4, which is much higher than GDY and NiCo2S4. The outstanding photocatalytic hydrogen production performance can be attributed to the S‐scheme GDY/NiCo2S4 heterostructure. The fluorescence results demonstrated that the incorporation of GDY significantly enhanced the efficiency of photoelectron‐hole transfer and prolonged the electron lifetime. The S‐scheme photogenerated charge transfer mechanism is verified through in situ irradiated X‐ray photoelectron spectroscopy. The present study introduces innovative concepts for the design of an S‐scheme heterojunction based on graphdiyne, aiming to enhance photocatalytic hydrogen production.

Isoreticular Preparation of Tetraphenylethylene‐based Multicomponent Metallacages towards Light‐Driven Hydrogen Production

AbstractMulticomponent metallacages can integrate the functions of their different building blocks to achieve synergetic effects for advanced applications. Herein, based on metal‐coordination‐driven self‐assembly, we report the preparation of a series of isoreticular tetraphenylethylene‐based metallacages, which are well characterized by multinuclear NMR, ESI‐TOF‐MS and single‐crystal X‐ray diffraction techniques. The suitable integration of photosensitizing tetraphenylethylene units as faces and Re catalytic complexes as the pillars into a single metallacage offers a high photocatalytic hydrogen production rate of 1707 μmol g−1 h−1, which is one of the highest values among reported metallacages. Femtosecond transient absorption and DFT calculations reveal that the metallacage can serve as a platform for the precise and organized arrangement of the two building blocks, enabling efficient and directional electron transfer for highly efficient photocatalytic performance. This study provides a general strategy to integrate multifunctional ligands into a certain metallacage to improve the efficiency of photocatalytic hydrogen production, which will guide the future design of metallacages towards photocatalysis.

Isoreticular Preparation of Tetraphenylethylene-based Multicomponent Metallacages towards Light-Driven Hydrogen Production.

Multicomponent metallacages can integrate the functions of their different building blocks to achieve synergetic effects for advanced applications. Herein, based on metal-coordination-driven self-assembly, we report the preparation of a series of isoreticular tetraphenylethylene-based metallacages, which are well characterized by multinuclear NMR, ESI-TOF-MS and single-crystal X-ray diffraction techniques. The suitable integration of photosensitizing tetraphenylethylene units as faces and Re catalytic complexes as the pillars into a single metallacage offers a high photocatalytic hydrogen production rate of 1707 μmol g-1 h-1, which is one of the highest values among reported metallacages. Femtosecond transient absorption and DFT calculations reveal that the metallacage can serve as a platform for the precise and organized arrangement of the two building blocks, enabling efficient and directional electron transfer for highly efficient photocatalytic performance. This study provides a general strategy to integrate multifunctional ligands into a certain metallacage to improve the efficiency of photocatalytic hydrogen production, which will guide the future design of metallacages towards photocatalysis.

ZnO/ZnS/CdS three-phase composite photocatalyst with a flower cluster structure: Research on its preparation and photocatalytic activity hydrogen production

The ZnO/ZnS/CdS three-phase composite photocatalyst with a flower cluster structure was successfully synthesized in three steps with ammonia as the hydrothermal solvent. The photocatalyst showed excellent photocatalytic activity for hydrogen production with a rate of photocatalytic hydrogen production up to 2.64 mmol h−1 g−1 and the photocatalyst also exhibited perfect stability, and the photoactivity displayed no significant degradation during continuous hydrogen production over nearly 72 h. Further detailed characterizations revealed that the CdS in the ZnO/ZnS/CdS photocatalyst uniformly wrapped on the surface of ZnS. The presence of ZnS improved the hydrogen generation overpotential of CdS in the ZnO/ZnS/CdS photocatalyst. The position of the valence band for ZnO in the ZnO/ZnS/CdS photocatalyst was more negative than that of CdS, so the photocatalytic oxidation reaction occurred in the valence band of ZnO rather than that of CdS. The above results greatly improved photocatalytic activity of hydrogen production and photocatalytic stability for the ZnO/ZnS/CdS photocatalyst.

Conjugated porous polymers regulated by thiophene and polycyclic aromatic hydrocarbons for photocatalytic water splitting toward hydrogen production

Rational design of organic semiconductors with wide visible light absorption and quick charge separation is of great significance for photocatalytic hydrogen production form water. In this work, the chemical structure of a linear conjugated polymer composed of ethynyl-linked benzene (B) and 2,1,3-benzothiadiazole (BT) is regulated by thiophene (TP) and polycyclic aromatic hydrocarbons [naphthalene (N) and anthracene (A)], and series of polymers including B-BT-TP-x, N-BT-TP-x and A-BT-TP-x (x = 0.2, 0.4, 0.6, 0.8) are synthesized. After thiophene and polycyclic aromatic hydrocarbon regulation, the polymers exhibit strong absorption in the whole visible light region of 400->650 nm and quick internal charge separation and transfer. Visible-light-driven photocatalytic hydrogen production rates of the synthesized polymers follow the order of B-BT (170.0 μmol/h) < B-BT-TP-0.6 (735.3 μmol/h) < N-BT-TP-0.4 (841.5 μmol/h) < A-BT-TP-0.6 (969.2 μmol/h) using 30 mg catalyst with 1.0 wt% Pt as cocatalyst. In addition, high apparent quantum yield (AQY) values of 8.04%, 5.58% and 0.95% under 550 nm, 650 nm and 700 nm monochromatic lights are obtained using A-BT-TP-0.6 catalyst. The present work provides new insights into design of advanced organic semiconductors for highly efficient photocatalytic solar energy conversion.

1T-WS2/NCN photocatalyst with unique trion behavior and cyano-defects: Photocatalytic hydrogen evolution and mechanistic insights

The interfacial catalytic reaction rate determines the hydrogen production performance of the photocatalyst. In this work, high specific surface area and cyano-defects g-C3N4 with 1T-WS2 as a co-catalyst was prepared to construct 1T-WS2/NCN photocatalytic system. The two-electron interfacial catalytic reaction pattern formed due to the unique trions behaviour of 1T-WS2 greatly enhanced the interfacial catalytic reaction rate. Under 180 min of light, the hydrogen production of the photocatalytic system could reach 5769.3 μmol/g, which was 91.6 times that of the pristine g-C3N4. It was found that the excellent electrical conductivity of 1T-WS2 with metallic nature and the low Gibbs free energy of its active edge facilitated the hydrogen production and release. Meanwhile, the unique trions behaviour of the two-electron catalytic reaction formed in 1T-WS2 is a significant factor in increasing the rate of photocatalytic hydrogen production. And the cyano-defects in g-C3N4 acts as an electron trap, which drives charge space separation and provides sufficient electrons for trions formation, facilitating two-electron catalytic hydrogen production. This study provides a new idea for the development of electron-hole separation to improve the photocatalytic hydrogen production activity, which has important theoretical significance and application value.

The construction of S-scheme heterostructure in ultrathin WS2/Zn3In2S6 nanosheets for enhanced photocatalytic hydrogen evolution

Metal sulfide based photocatalysts are considered to be economic, environmentally benign and renewable. The rapid recombination of photogenerated electrons and holes and low solar energy utilization efficiency, however, remain a huge bottleneck. Herein, two-dimensional/two-dimensional (2D/2D) S-scheme WS2/Zn3In2S6 heterostructure with ultrathin nanosheets intervening between neighboring component has been designed. The large and intimate S-scheme heterojunctions facilitate interfacial charge separation/transfer and optimize the available redox potential. Besides, the ultrathin 2D/2D heterostructure ensures large specific surface area, maximized interface synergistic interaction, and effective exposure of surface active sites. As a result, 2 wt% WS2/Zn3In2S6 exhibits a high photocatalytic hydrogen production rate of 30.21 mmol·g−1·h−1 under simulated solar light illumination with an apparent quantum efficiency of 56.1% at 370 nm monochromatic light, far exceeding pristine Zn3In2S6 (6.65 mmol·g−1·h−1). Our work underscores the significance of integrating morphology engineering and S-scheme heterojunctions design for high-efficient and low-cost photocatalysts.

Ni-doped CdSe/ZnSnO3 double-shell nanocubes heterojunction for efficient photocatalytic hydrogen evolution

In order to alleviate environmental pollution and energy crisis caused by the excessive use of fossil fuels, photocatalytic water splitting to produce hydrogen as an alternative fuel has attracted widespread attention. The construction of heterojunction photocatalyst is considered to be one of the effective ways to enhance the photocatalytic hydrogen production efficiency. In this study, Ni-doped CdSe was modified on the surface of hollow ZnSnO3 double-shell nanocubes. The obtained Cd0.9Ni0.1Se/ZnSnO3 possessed high photocatalytic activity under visible light irradiation. The photocatalytic hydrogen production rate could reach to 6458.0 μmol/g/h. The successful construction of hollow Cd0.9Ni0.1Se/ZnSnO3 double-shell type-I heterojunction increased visible light absorption, shortened the charge transport distance, and inhibited the recombination of electron-hole pairs, thus enhancing the photocatalytic hydrogen production performance of Cd0.9Ni0.1Se/ZnSnO3. It provided the idea for promoting the design of solar to chemical energy conversion and the effective guidance for constructing a high-efficient and stable photocatalyst.

Novel in-situ composites of chlorine-doped CQDs and g-C3N4 with improved interfacial connectivity and accelerated charge transfer to enhance photocatalytic degradation of tetracycline and hydrogen evolution

The photocatalytic performance of graphite-phase carbon nitrides (g-C3N4) composites is severely limited by poor interfacial connectivity and a narrow visible light response range. Although carbon quantum dots (CQDs) can enhance the visible light absorption of g-C3N4, it is difficult to produce effective interfacial connectivity due to their different properties. Herein, a novel “in-situ composite modified by chlorine-doped CQDs” strategy was proposed to further enhance the photocatalytic redox capability of g-C3N4. Specifically, chlorine-doped CQDs (Cl-CQDs) were prepared from mulberry branch powder and sulfoxide chloride directly, and the novel metal-free photocatalyst (Cl-CCN) was prepared by in-situ compounding the Cl-CQDs with g-C3N4. Cl-CCN shows superior photocatalytic tetracycline degradation rate (0.0269 min−1) and hydrogen production rate (1397.5 µmol g−1h−1), which are 14.9 and 2.75 times higher than those of g-C3N4, respectively. The characterization and DFT calculation results reveal that the C − Cl covalent bonds serve as fast electronic channels to bridge the hydrophilic Cl-CQDs and hydrophobic g-C3N4 and significantly enhance the interfacial coupling and charge transfer. On this basis, a possible mechanism for tetracycline degradation and hydrogen production photocatalyzed by Cl-CCN is proposed. This study provides a concise and economical method for modifying and enhancing the photocatalytic activity of composites CQDs/g-C3N4.

Synthesis of Multiple Emission Carbon Dots from Dihydroxybenzoic Acid via Decarboxylation Process.

Carbon dots (CDs), as a new zero-dimensional carbon-based nanomaterial with desirable optical properties, exhibit great potential for many application fields. However, the preparation technique of multiple emission CDs with high yield is difficult and complex. Therefore, exploring the large-scale and straightforward synthesis of multicolor CDs from a simple carbon source is necessary. In this work, the solvent-free method prepares a series of multicolor emission CDs from dihydroxybenzoic acid (DHBA). The maximum emission wavelengths are 408, 445, 553, 580, and 610 nm, respectively, covering the visible light region. The 2,4- and 2,6-CDs possess the longer emission wavelength caused by the 2,4-, and 2,6-DHBA easily undergo decarboxylation to form the larger sp2 domain graphitized structure. These CDs incorporated with g-C3N4 can significantly improve the photocatalytic water-splitting hydrogen production rate by extending the visible light absorption and enhancing the charge separation efficiency. The long-wavelength emission CDs can further enhance photocatalytic activity primarily by improving visible light absorption efficiency.

Constructing CdIn2S4/ZnS type-I band alignment heterojunctions by decorating CdIn2S4 on ZnS microspheres for efficient photocatalytic H2 evolution

In this study, a series of promising binary hybrid heterojunction CdIn2S4/ZnS (CIS/ZnS) were constructed via a facile hydrothermal method. Credible characterization methods including powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–vis diffuse reflectance spectra (DRS) were carried out to investigate the physicochemical properties the as-obtained photocatalysts. Photocatalytic water splitting for hydrogen evolution was performed to evaluate the photocatalytic activity of the photocatalyst. The results indicate that the light-harvesting ability could be markedly enhanced by decorating CdIn2S4 on ZnS microspheres. Compared with the pristine CdIn2S4 and ZnS, the hybrid photocatalysts present more efficient photocatalytic hydrogen production performance. Among composite photocatalysts, the 5% CIS/ZnS sample manifests the highest photocatalytic hydrogen production rate of 10.80 mmol g−1 h−1, which is 2.6 and 5.4 times higher than that of ZnS and CdIn2S4, respectively. Moreover, a type-I band alignment mechanism was prudently put forward to interpret the photocatalytic hydrogen generation activity. The boosted photocatalytic hydrogen evolution activities of CIS/ZnS can be attributed to the enhanced light-harvesting ability, efficient separation and transfer of the photo-induced charge carriers, and inhibition of electrons and holes recombination of binary hybrid CIS/ZnS photocatalysts.

Facile synthesis of ultrathin g-C3N4 nanosheets modified with N-doped carbon dots: Enhanced photocatalytic hydrogen production activity and mechanism insight

In this study, nitrogen-doped carbon dots (NCDs) modified ultrathin carbon nitride (g-C3N4) nanosheets were synthesized by a simple secondary calcination method, which realizes efficient photocatalytic hydrogen production. The secondary calcination process can not only thermally exfoliate g-C3N4 into ultrathin nanosheets, but also uniformly anchor NCDs (∼3 nm) on the surface of g-C3N4. The photocatalytic results manifested that a very small amount of NCDs (0.5 wt%) loading on g-C3N4 could achieve a high photocatalytic hydrogen production rate (5.21 mmol g−1 h−1). The reasons for the enhanced photocatalytic activity were analyzed. The ultrathin g-C3N4 nanosheets facilitated the migration of photogenerated carriers. Moreover, NCDs/g-C3N4 exhibited enhanced visible light absorption owing to the up-conversion fluorescence effect of NCDs and the narrow band gap caused by the decoration of NCDs. Furthermore, NCDs as electron acceptors can promote carrier separation. This combination strategy provides a basis for the synthesis of inexpensive, metal-free, and efficient carbon-based photocatalysts.

2D/2D Z-scheme photocatalyst of g-C3N4 and plasmonic Bi metal deposited Bi2WO6: Enhanced separation and migration of photoinduced charges

An ideal photocatalyst should have high redox capacity, efficient charge separation, and large reaction surface area. However, it is an extreme challenge to construct a photocatalytic system with above three merits. Herein, the g-C3N4/[email protected]2WO6 composite photocatalyst was prepared by simple wet chemical method. Then the separation pathway of photoinduced charges through the interface was explored by XPS, EPR and active species capture experiments, confirming that the Z-scheme charge transfer route was followed. The optimized composite photocatalyst exhibited the photocatalytic hydrogen production rate of 1219.3 μmol h−1g−1, which is 2.29 times that of pure g-C3N4 (533.4 μmol h−1g−1). Moreover, the photocatalytic degradation rates of RhB and TC were 82.43% and 66.7%, respectively, which were 7.55 times and 1.92 times that of pure Bi2WO6. Ultimately, the enhanced photocatalytic performances were attributed to the synergistic effect of 2D/2D coupling interface and the deposited metal Bi, which not only benefited the efficient charge separation and fast charge migration but also provided the large reaction surface area. In addition, surface plasmon resonance effect of metal Bi can boost the visible light absorption and broaden the light absorption range to the full spectrum. Our study provides a new idea to design high-performance Z-scheme photocatalyst for highly efficient utilization of solar energy.

Regulating Intermediate Concentration to Synthesize Highly Crystalline g‐C3N4 under Spontaneous Ultrahigh Pressure

AbstractImproving polymerization and crystallization properties has become a key point to maximize the intrinsic photocatalytic performance of graphitic carbon nitride (g‐C3N4), however, the critical roles of intermediates in the polymerization and crystallization process are not clear. Herein, highly crystalline g‐C3N4 is obtained by calcinating different amount of dicyandiamide in a closed environment. Ultrahigh atmospheric pressure up to 6.2 MPa can be spontaneously formed due to the produced gaseous intermediates. The best crystallization properties were achieved when 1.8 g of dicyandiamide was used. The photocatalytic hydrogen production rate reaches 9241.3 μmol ⋅ g−1 ⋅ h−1, which is improved by about 12.5 times by comparison. The crystallization and hydrogen production activities cannot be enhanced only by adding an initial gas pressure meanwhile keeping the quality of dicyandiamide constant, confirming that the intermediate concentration determines the polymerization and hydrogen production performance of g‐C3N4. This study is important to improve the intrinsic photocatalytic performance of g‐C3N4 and the composites.

Cs-Cu-Cl perovskite quantum dots for photocatalytic H2 evolution with super-high stability

Metal halide perovskites with broad optical absorption and long carrier lifetime are considered as ideal photocatalysts. However, their poor stability in water greatly impedes their application in photocatalytic H2 evolution because they lose their crystalline structure in water. Herein, we proclaim a new class of photocatalysts: all-inorganic Cs-Cu-Cl perovskite quantum dots (QDs). It exhibits a high photocatalytic hydrogen production rate of ∼ 3.1 mmol/g/h without any cocatalyst under AM 1.5-G solar irradiation (100 mW/cm2). Especially, it remains the high activity for up to 330 h without apparent deterioration of the hydrogen production rate. Density functional theory (DFT) calculations reveal that the Cu site works as the electron and proton absorption sites as the H2 production active center. To our best knowledge, there is no report of metal halide perovskites as water-stable photocatalysts. This work opens an innovative way for guiding the exploration of metal halide perovskites photocatalysts for stable photocatalytic H2 evolution.

NiO co-catalyst modification ZnIn2S4 driving efficient hydrogen generation under visible light

Photocatalytic hydrogen production is considered as a good countermeasure to solve the energy crisis, but the existing photocatalysts have very slow electron-hole separation efficiency. How to design a photocatalyst with high photogenerated carrier separation efficiency has become a difficult rproblem. The efficiency of photogenerated carrier separation can significantly improve by precious metal co-catalyst, but its further development is limited by high cost. In this work, non-precious metal NiO is used as a co-catalyst and formed heterojunction with ZnIn2S4 (ZIS) as a cocatalyst, which significantly enhances the efficiencies of photogenerated carrier separation. According to the results of transient photocurrent (TPR) and Photoluminescence (PL), ZnIn2S4/NiO (ZIS/NiO) has the fastest photogenerated carrier separation rate when the mass fraction of NiO is 3%, which is about 5 times than pure ZIS. At the same time, the highest photocatalytic hydrogen production rate of 5 mmolg−1 h−1 was achieved under visible-light (λ ≥ 420 nm), which was 6.2 times more than pure ZIS (0.804 mmolg−1 h−1). This work offers a new option for low cost, high performance co-catalyst.

A Novel ZnO/Co3O4 Nanoparticle for Enhanced Photocatalytic Hydrogen Evolution under Visible Light Irradiation

In recent years, ZnO/Co3O4 nanoparticles (NPs) have been reflected as typical of the most promising photocatalysts utilized in the field of photocatalysis for potentially solving energy shortages and environmental remediation. In this work, a novel ZnO/Co3O4 NP photocatalyst was fabricated and utilized for photocatalytic hydrogen evolution with visible light activity. ZnO/Co3O4 NPs display an improved photocatalytic hydrogen production rate of 3963 μmol/g through a five-hour test under visible light activity. This is much better than their single components. Hence, bare ZnO NPs loaded with 20 wt% Co3O4 NPs present optimum efficiency of hydrogen evolution (793.2 μmol/g/h) with 10 vol% triethanolamine (TEOA), which is 11.8 times that of pristine ZnO NPs. An achievable mechanism for improved photocatalysis is endowed in terms of the composite that promotes the operative separation rate of charge carriers that are produced by visible light irradiation. This study yields a potential process for the future, proposing economical, high-function nanocomposites for hydrogen evolution with visible light activity.

Light and Mass Transport Computations Guide the Fabrication of 3D-Structured TiO2 and Au/TiO2 Aerogel Photocatalysts for Efficient Hydrogen Production in the Gas Phase

Efficient mass transfer and light utilization are essential for high photocatalytic production rates. Here, we present a hierarchical three-dimensional (3D)-printed aerogel photocatalyst that unites both aspects by taking inspiration from the light scattering in clouds during photochemical processes and from mass transfer in plants during photosynthesis. We combine the geometric freedom of additive manufacturing with computational fluid dynamics and Monte Carlo simulations to guide the implementation of a self-supported aerogel in a continuous gas flow reactor. Here, 3D microstructuring reduced the pressure drop of a monolithic aerogel by 5 orders of magnitude without compromising the gas permeation and the light-harvesting efficiency of the intrinsic nanoporous material. We match the macroscopic thickness with the ultraviolet (UV) light penetration depth and show that the 3D aerogel of 1.1 mm thickness improves photocatalytic hydrogen production rates relative to the nanoparticle powder by a factor of five from 1.3 to 6.6 μmol g–1 h–1 for TiO2 and from 30.0 to 141.8 μmol g–1 h–1 for Au/TiO2, respectively. Ultimately, our approach can be applied for other nanomaterials to boost the overall performance of a variety of photochemical processes and reactor designs.

Single-Atom Cu Channel and N-Vacancy Engineering Enables Efficient Charge Separation and Transfer between C3N4 Interlayers for Boosting Photocatalytic Hydrogen Production

Polymeric carbon nitride (C3N4) has attracted great attention in photocatalysis due to its low-cost, visible-light response, and environment-friendly merits. However, the catalytic efficiency of pristine bulk C3N4 is severely limited by its poor photoinduced electron/hole pair separation and interlayer charge transport. Herein, single-atom Cu is bridged into C3N4 sheet interlayers through the thermal condensation of self-assembly supramolecules of Cu precursors and melamine–cyanuric acid monomers. Simultaneously, N vacancies are engineered into C3N4 only by gradient temperature. The single-atom Cu bridges serve as electron channels to promote photoinduced electron/hole pair separation and interlayer charge transport. The experimental results and calculations demonstrate that N vacancies break the symmetry of pristine C3N4, allowing more electrons to pass through the delocalized π-conjugated network of C3N4 to Cu sites, which facilitates charge transfer between C3N4 layers, resulting in more effective separation of electron/hole pairs, optimal charge distribution, and lower hydrogen evolution barrier. As a result, the photocatalyst at a stationary point with a 1 wt % Pt cocatalyst presents a high visible-light photocatalytic hydrogen production rate (11.23 mmol g–1 h–1), reaching a high apparent quantum yield of 31.60% at 420 nm. It is noted that the photocatalyst still exhibits a high hydrogen production rate of 605.15 μmol g–1 h–1 in the absence of the Pt cocatalyst.

Enhanced photocatalytic performance of hollow spherical CdS QDs@ZrO2–TiO2 composites with double Z-scheme heterostructures

In this paper, CdS QDs@ZrO2–TiO2 hollow spherical composites with double Z-scheme heterostructure modified by CdS QDs were prepared by the sol–gel method and vacuum impregnation method using polystyrene (PS) microspheres synthesized by the self-assembly technique as templates. A series of characterization results show that CdS QDs@ZrO2–TiO2 composites treated by PS microspheres have the structure of hollow spheres with uniform size and orderly arrangement. Moreover, the double Z-scheme heterojunction formed between CdS QDs, ZrO2, and TiO2 in the composite can optimize the charge transfer path and improve the charge separation efficiency. Results of the photodegradation and the photo-splitting water of CdS QDs@ZrO2–TiO2 composites show that, compared with other systems, CdS QDs@ZrO2–TiO2 composites have the highest photocatalytic degradation rate of crystal violet, and meanwhile, the photocatalytic hydrogen production rate of the composite under simulated sunlight is more than 100 times that of TiO2. The good absorption of visible light, the successful construction of double Z-scheme heterojunction, and the unique hollow sphere structure of CdS QDs@ZrO2–TiO2 composites are the key factors for enhanced photocatalytic performance.