The development of the Internet of Things (IoT) technology and their integration in smart cities have changed the way we work and live, and enriched our society. However, IoT technologies present several challenges such as increases in energy consumption, and produces toxic pollution as well as E-waste in smart cities. Smart city applications must be environmentally-friendly, hence require a move towards green IoT. Green IoT leads to an eco-friendly environment, which is more sustainable for smart cities. Therefore, it is essential to address the techniques and strategies for reducing pollution hazards, traffic waste, resource usage, energy consumption, providing public safety, life quality, and sustaining the environment and cost management. This survey focuses on providing a comprehensive review of the techniques and strategies for making cities smarter, sustainable, and eco-friendly. Furthermore, the survey focuses on IoT and its capabilities to merge into aspects of potential to address the needs of smart cities. Finally, we discuss challenges and opportunities for future research in smart city applications.

物联网 (IoT) 技术的发展及其在智慧城市中的融合改变了我们的工作和生活方式，丰富了我们的社会。然而，物联网技术带来了一些挑战，例如能源消耗增加，并在智慧城市中产生有毒污染和电子垃圾。智慧城市应用必须是环保的，因此需要向绿色物联网迈进。绿色物联网带来生态友好的环境，这对智慧城市来说更具可持续性。因此，必须解决减少污染危害、交通浪费、资源使用、能源消耗、提供公共安全、生活质量以及维持环境和成本管理的技术和策略。本次调查的重点是全面回顾使城市变得更智能、更可持续和更环保的技术和策略。此外，该调查侧重于物联网及其融合到满足智慧城市需求的潜力方面的能力。最后，我们讨论了未来智慧城市应用研究的挑战和机遇。